Specify protocol when using host.docker.internal proxy

[mathbunnyru]

Describe your changes

Issue ticket if applicable

Checklist (especially for first-time contributors)

• I have performed a self-review of my code
• If it is a core feature, I have added thorough tests
• I will try not to use force-push to make the review process easier for reviewers
• I have updated the documentation for significant changes

[mathbunnyru]

I built an image locally and then ran docker run -it --rm -e HTTPS_PROXY=host.docker.internal -e HTTP_PROXY=host.docker.internal quay.io/jupyter/base-notebook

This gives an error:

  File "/opt/conda/lib/python3.12/site-packages/httpx/_config.py", line 214, in __init__
    raise ValueError(f"Unknown scheme for proxy URL {url!r}")
ValueError: Unknown scheme for proxy URL URL('host.docker.internal')