Run Gradle 5 tests only for JDK versions < 13

[schalkms]

No description provided.

[codecov-io]

Codecov Report

Merging #2143 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #2143      +/-   ##
============================================
+ Coverage      80.5%   80.52%   +0.02%     
  Complexity     2017     2017              
============================================
  Files           336      336              
  Lines          5801     5808       +7     
  Branches       1063     1063              
============================================
+ Hits           4670     4677       +7     
  Misses          564      564              
  Partials        567      567

Impacted Files	Coverage Δ	Complexity Δ
...ch/detekt/api/internal/ValidatableConfiguration.kt	88.57% <0%> (+2.85%)	0% <0%> (ø)	⬇️

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[BraisGabin]

return if (jdkVersion < 13) {
  listOf("5.0", "6.0.1")
} else {
  listOf("6.0.1")
}

I think that it's easier to know which versions are going to be tested like this. You could even create two consts: GRADLE_5 and GRADLE_6. But I think that the strings helps more to the readability than the constants to the maintanability.

[arturbosch]

Agree here in terms of readability:

private fun getGradleVersionsUnderTest() =
    if (jdkVersion() < 13) {
        listOf("5.0", "6.0.1")
    } else {
        listOf("6.0.1")
    }