fix(tests): bump to JUnit6 and fix build config

[jponge]

Fixes #1969

[jponge]

/cc @tsegismont @Ladicek as we discussed this earlier today

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.08%. Comparing base (67fe9de) to head (0be2169).
⚠️ Report is 36 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1978      +/-   ##
============================================
- Coverage     89.17%   89.08%   -0.10%     
+ Complexity     3068     3065       -3     
============================================
  Files           409      409              
  Lines         13068    13068              
  Branches       1650     1650              
============================================
- Hits          11653    11641      -12     
- Misses          803      810       +7     
- Partials        612      617       +5     

see 8 files with indirect coverage changes

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