Similar to python/python-docs-theme#108.

Fix the problems we saw at #1034 (comment) when the CSS file changed but browsers kept the old version cached for 24 hours.

Append a ?digest=hash to the end of the pydoctheme.css, computed from the file contents, so when a new CSS file is deployed, the old one is no longer used from the browser cache.

For example:

<link rel="stylesheet" type="text/css" href="_static/devguide_overrides.css?digest=951d6a16b747d96c03796069dbeb516764307ae2" />

This is based on how @pradyunsg's Furo theme does it:

https://github.com/pradyunsg/furo/blob/193643fdb6787501195555244f4a9e953ef544bb/src/furo/__init__.py#L149-L161

Thanks @pradyunsg!

Demo

View the source of pages at https://cpython-devguide--1054.org.readthedocs.build/.

Furo's css already has a digest, this PR adds it to devguide_overrides.css.

Check the colours load in the EOL chart at https://cpython-devguide--1054.org.readthedocs.build/versions/