PHPUnit 9 → 10

[thomascorthals]

Major changes affecting us:

• setUpBeforeClass()/tearDownAfterClass() can no longer perform assertions. Tests of correct configuration have been moved to separate test functions.
• Changes in mocks necessitate a different approach, a.o. when testing traits.
• Data providers always have to be declared static.

[thomascorthals]

Looks like I broke the codecov integration. Converting to draft for now.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.72%. Comparing base (9cdf3dd) to head (9606926).
Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1144      +/-   ##
==========================================
- Coverage   97.75%   97.72%   -0.04%     
==========================================
  Files         400      403       +3     
  Lines       10524    10578      +54     
==========================================
+ Hits        10288    10337      +49     
- Misses        236      241       +5     

Flag	Coverage Δ
unittests	97.72% <ø> (-0.04%)	⬇️

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