ci: Check strictly for success

[szokeasaurusrex]

Previously, some statuses other than success (e.g. cancelled) were considered passing for the check_required_tests job. See, for example, this job run, where several tests timed out, ending with cancelled status, but the final check passed.

We can instead check directly against the success status, to strictly enforce that all tests must pass.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.69%. Comparing base (89e624a) to head (14dfa0a).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4589      +/-   ##
==========================================
- Coverage   80.71%   80.69%   -0.02%     
==========================================
  Files         156      156              
  Lines       16507    16507              
  Branches     2806     2806              
==========================================
- Hits        13323    13321       -2     
- Misses       2296     2297       +1     
- Partials      888      889       +1     

see 1 file with indirect coverage changes