Avoid executing the tests twice (once through JUnit, once through kover)

[opatry]

Follow-up of #119 and #193:

• How would it be possible to run tests only once for both JUnit & kover? Is it desirable?
• Maybe also split main build in several Jobs?
  • Desktop/Jvm on one side
  • Android on the other
  • Kover in parallel?
  • ⚠ Might impact CI minutes consumption (rebuilding the same things several times in parallel), is it an issue (overall pipeline should be shorter, but added consumed minutes increased) for open source projects?

[opatry]

Now that the unit tests & coverage steps are split in 2 separates jobs, this becomes kinda pointless (see #243).

I still like having 2 different status, all tests succeeded on 1 side, coverage thresholds are fine on the other side.