Fix CI issues with readthedocs, python 3.7, and broken clip test

[reinecke]

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A grab-bag of fixes for issues causing failing CI, including:

1. Updated the CI to run linux python 3.7 checks on ubuntu 22.04 - the last version that includes python 3.7 in github runners- (see this version manifest for reference.
2. Added an explicit path for the sphinx configuration in accordance with this blog post.
3. Updated some clip unittests to account to effects and markers being included in the __str__ and __repr__ methods as of Add effect and marker initialization to Clip #1808