CI pipeline not working properly

[mathemancer]

Description

Currently, the CI pipeline is:

• skipping tests but treating them as having succeeded when an internal mathesar contributor makes a PR under certain conditions
• Not allowing merging in some conditions since tests skipped due to branch/path restrictions are marked pending rather than success
• Broken whenever backend tests need to run since the setup defined in run-pytest.yml is defective

Expected behavior

The CI pipeline should always:

• Run tests relevant to any changed code before merging
• Avoid hanging due to non-runs of irrelevant tests
• Use a correct setup for python testing.

Additional context

Blocking #3243 , #3245 , and potentially others.