ci: Add unit tests required check

[philipphofmann]

Use dorny path filters to have one single job failing or succeeding when the unit tests passed or were skipped so we can enable unit tests as required checks for PRs.

Fixes GH-5868

PR with only a Changelog entry let's the job unit test pass #5891.

When cancelling unit tests jobs fail

https://github.com/getsentry/sentry-cocoa/actions/runs/16907162839/job/47899511411

When a few unit tests fail also the main unit test job fails

#skip-changelog

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.681%. Comparing base (f37e3fe) to head (e0e10cc).
⚠️ Report is 6 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #5885       +/-   ##
=============================================
+ Coverage   86.656%   86.681%   +0.024%     
=============================================
  Files          423       423               
  Lines        36505     36505               
  Branches     17274     17277        +3     
=============================================
+ Hits         31634     31643        +9     
+ Misses        4824      4815        -9     
  Partials        47        47               

see 7 files with indirect coverage changes

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[philprime]

LGTM, let's give this a shot and fix it ASAP if we get blocked.