ci: Run only API tests affected by changes in PRs and Upgrade GHA runners

[novakzaballa]

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Changes

Use pytest-testmon to only execute API tests affected by changed files. Also upgrade GHA runners for this specific job.

How did you test this code?

API Tests executed as expected. Also testing manually using this PR to ensure that only tests affected by changes are exectured.

Implementation notes

Notice that for retrieving the cache we use github.event.pull_request.base.sha as the final part of the cache key, and when we save the tesmon database file to the cache we use github.sha. That is because we restore cache only on PR events while we save the cache only on the push to main event, and github.event.pull_request.base.sha on the PR event context should be the same as github.sha of the base branch on the push event context.

Also, notice that we are using absolute paths for storing/retrieving the tesmon database file to/from the cache. We do that because if we use a relative path it will not be relative to the working directory, but to the workspace directory, which can vary depending on the context, so in this particular case I think it is better to stick to the absolute path. For more details refer to the comments below.

[vercel]

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[github-actions]

Uffizzi Ephemeral Environment Deploying

☁️ https://app.uffizzi.com/github.com/Flagsmith/flagsmith/pull/2867

⚙️ Updating now by workflow run 6644560383.

What is Uffizzi? Learn more!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b0ef013) 95.60% compared to head (e1098fb) 95.60%.
Report is 14 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2867   +/-   ##
=======================================
  Coverage   95.60%   95.60%           
=======================================
  Files        1009     1009           
  Lines       28904    28910    +6     
=======================================
+ Hits        27634    27640    +6     
  Misses       1270     1270           

see 5 files with indirect coverage changes

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