Add junit6 to spock-testkit

[AndreasTu]

This shall ensure the execution with JUnit 6 is possible.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.09%. Comparing base (93344d9) to head (0cbd2c9).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2236      +/-   ##
============================================
+ Coverage     82.07%   82.09%   +0.02%     
  Complexity     4756     4756              
============================================
  Files           465      465              
  Lines         14871    14871              
  Branches       1878     1878              
============================================
+ Hits          12205    12208       +3     
+ Misses         1978     1975       -3     
  Partials        688      688              

see 2 files with indirect coverage changes

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[Vampire]

Wouldn't it instead make sense to have a second test task in spock-specs that runs with JUnit 6 so that all tests are executed? There could also be problems in specific paths, like when using data driven tests and so on.

[AndreasTu]

We could do that, but I did not want to double the test-execution time.
I would be more specific, if there is a regression add a test for JUnit6 there instead of executing everything twice.

[Vampire]

@leonard84 what's your take on this? :-)

[leonard84]

If we want to test the SpockEngine compatibility, then I'd reuse spock-testkit.

[AndreasTu]

@leonard84 done