Tweak junit execution for parallel testing (#3001)

- [x] Set junit parameters in maven test
  - [x] Local IntelliJ test run: 33s -> 15s 
  - [x] Local `maven test` run: 58s -> 30s
  - [x] CI run
- [x] JDK8:
[02:10m](https://github.com/vavr-io/vavr/actions/runs/13807668590/job/38621833526#step:4:4018)
->
[02:00m](https://github.com/vavr-io/vavr/actions/runs/13809442865/job/38627485133?pr=3001#step:4:4021)
- [x] JDK11:
[01:46m](https://github.com/vavr-io/vavr/actions/runs/13807668590/job/38621834088#step:4:5217)
->
[01:21m](https://github.com/vavr-io/vavr/actions/runs/13809442865/job/38627485605?pr=3001#step:4:5196)
- [x] JDK23:
[01:35m](https://github.com/vavr-io/vavr/actions/runs/13807668590/job/38621835881#step:4:5207)
->
[01.10m](https://github.com/vavr-io/vavr/actions/runs/13809442865/job/38627487693?pr=3001#step:4:5168)

Local data gathered on MacBook Pro M1 Max, 64GB RAM

Author: bvkatwijk

vavr/src/test/resources/junit-platform.properties

@@ -0,0 +1,2 @@
+junit.jupiter.execution.parallel.enabled = true
+junit.jupiter.execution.parallel.mode.default = concurrent