RFR: build: update JUnit to 5.6.2

[Erik Helin]

Hi all,

please review this patch that updates JUnit (API and engine) to 5.6.2 and JUnit
platform to 1.6.2.

Testing:
- `sh gradlew test` passes on Linux x64

Thanks,
Erik

-------------

Commit messages:
 - build: update JUnit to 5.6.2

Changes: https://git.openjdk.java.net/skara/pull/613/files
 Webrev: https://webrevs.openjdk.java.net/skara/613/webrev.00
  Stats: 7 lines in 2 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/skara/pull/613.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/613/head:pull/613

PR: https://git.openjdk.java.net/skara/pull/613