Describe the bug

Sphinx linkcheck fails with a 403 Client Error: Forbidden error on every GitHub Docs site URL, even though the links are correct and work fine.

How to Reproduce

1. Create a new sphinx project with sphinx-quickstart.
2. Add a docs.github.com URL to the index.rst file, like so:

   `GitHub Hello World <https://docs.github.com/en/get-started/quickstart/hello-world>`_

3. Run make linkcheck

And you can verify that the above link works fine:

https://docs.github.com/en/get-started/quickstart/hello-world

Expected behavior

There should be no broken link error.

Your project

https://foundations.projectpythia.org/

Screenshots

No response

OS

Mac OS 11.6.5 and linux

Python version

3.10.4

Sphinx version

4.2.0+

Sphinx extensions

No response

Extra tools

No response

Additional context

No response