Build fails under these conditions: mkdocs 1.4.0, material 8.5.3+insiders.4.24.0, `consent` present, `repo_url` missing

### Contribution guidelines

- [X] I've read the [contribution guidelines](https://github.com/squidfunk/mkdocs-material/blob/master/CONTRIBUTING.md) and wholeheartedly agree

### I've found a bug and checked that ...

- [X] ... the problem doesn't occur with the `mkdocs` or `readthedocs` themes
- [X] ... the problem persists when all overrides are removed, i.e. `custom_dir`, `extra_javascript` and `extra_css`
- [X] ... the documentation does not mention anything about my problem
- [X] ... there are no open or closed issues that are related to my problem

### Description

When I attempt to build my site, I get the following error

```
$ python3 -m mkdocs serve

INFO     -  Building documentation...
INFO     -  Cleaning site directory
Traceback (most recent call last):
  File "/opt/homebrew/Cellar/python@3.10/3.10.6_1/Frameworks/Python.framework/Versions/3.10/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/opt/homebrew/Cellar/python@3.10/3.10.6_1/Frameworks/Python.framework/Versions/3.10/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/mkdocs/__main__.py", line 301, in <module>
    cli()
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/click/core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/click/core.py", line 1055, in main
    rv = self.invoke(ctx)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/click/core.py", line 1657, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/click/core.py", line 760, in invoke
    return __callback(*args, **kwargs)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/mkdocs/__main__.py", line 234, in serve_command
    serve.serve(dev_addr=dev_addr, livereload=livereload, watch=watch, **kwargs)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/mkdocs/commands/serve.py", line 82, in serve
    builder(config)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/mkdocs/commands/serve.py", line 75, in builder
    build(config, live_server=live_server, dirty=dirty)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/mkdocs/commands/build.py", line 320, in build
    _build_theme_template(template, env, files, config, nav)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/mkdocs/commands/build.py", line 118, in _build_theme_template
    output = _build_template(template_name, template, files, config, nav)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/mkdocs/commands/build.py", line 97, in _build_template
    output = template.render(context)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/jinja2/environment.py", line 1301, in render
    self.environment.handle_exception()
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/jinja2/environment.py", line 936, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/material/404.html", line 4, in top-level template code
    {% extends "main.html" %}
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/material/main.html", line 4, in top-level template code
    {% extends "base.html" %}
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/material/base.html", line 211, in top-level template code
    {% include "partials/consent.html" %}
  File "/Users/bgorman/GormAnalysis Dropbox/Ben Gorman/Projects/Python/material-broken/venv/lib/python3.10/site-packages/material/partials/consent.html", line 10, in top-level template code
    {% if "github.com" in config.repo_url %}
TypeError: argument of type 'NoneType' is not iterable
```

The error is due to Jinja's `in` operator being used with a None value inside `consent.html`. Specifically, this line

```
    {% if "github.com" in config.repo_url %}
TypeError: argument of type 'NoneType' is not iterable
```

If these conditions are present, you should be able to reproduce this:

- mkdocs 1.4.0,
- material 8.5.3+insiders.4.24.0
- `consent` present in `mkdocs.yml`
- `repo_url` not present in `mkdocs.yml`

Strangely, this only occurred when I upgraded to mkdocs 1.4.0.

### Expected behaviour

Site should build without error.

### Actual behaviour

See the error above.

### Steps to reproduce

I've published an [example repo you can clone](https://github.com/ben519/material-broken) to reproduce this error.

```
git clone https://github.com/ben519/material-broken.git
cd material-broken

export GH_TOKEN=XYZToken
python3 -m pip install mkdocs git+https://${GH_TOKEN}@github.com/squidfunk/mkdocs-material-insiders.git --upgrade

python3 -m mkdocs serve
```

### Package versions

Python 3.10.6
mkdocs, version 1.4.0
Version: 8.5.3+insiders.4.24.0

### Configuration

```yaml
site_name: ABC
# repo_url: https://github.com/squidfunk/mkdocs-material  # uncomment this line and the build works

theme:
  name: material

extra:
  consent:
    title: Cookie consent
    description: hello world

nav:
  - Home: index.md
  - Dogs:
    - dogs/index.md
    - Golden Retrievers:
      - Golden Retrievers: dogs/golden-retrievers/index.md
      - Movies: dogs/golden-retrievers/movies.md
```


### System information

Mac OS 12.6
Chrome Version 105.0.5195.125 (Official Build) (arm64)

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Build fails under these conditions: mkdocs 1.4.0, material 8.5.3+insiders.4.24.0, `consent` present, `repo_url` missing #4430

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Build fails under these conditions: mkdocs 1.4.0, material 8.5.3+insiders.4.24.0, consent present, repo_url missing #4430

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I've found a bug and checked that ...

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Build fails under these conditions: mkdocs 1.4.0, material 8.5.3+insiders.4.24.0, `consent` present, `repo_url` missing #4430