4.x: Convert from JUnit 4 to JUnit 6

[akarnokd]

It had to be done in one swoop or else some remnants could have caused issues.

• Added missing standard scheduler tests to ParallelScheduler, SharedScheduler
• Added missing SchedulerIntrospection to various task holder classes

Resolves #8079

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 5.006 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

build.gradle: 5.006

✅ No secrets or suspicious high-entropy strings found.

Mid-4 beauty heuristic in action — powered by our entropy chats! 😊

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.33%. Comparing base (109a56c) to head (238b58c).
⚠️ Report is 1 commits behind head on 4.x.

Additional details and impacted files

@@             Coverage Diff              @@
##                4.x    #8202      +/-   ##
============================================
- Coverage     98.34%   98.33%   -0.02%     
- Complexity     6772     6783      +11     
============================================
  Files           777      777              
  Lines         48464    48506      +42     
  Branches       6563     6570       +7     
============================================
+ Hits          47663    47696      +33     
- Misses          605      610       +5     
- Partials        196      200       +4     

☔ View full report in Codecov by Harness.
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[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 5.006 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

build.gradle: 5.006

✅ No secrets or suspicious high-entropy strings found.

Mid-4 beauty heuristic in action — powered by our entropy chats! 😊

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 5.006 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

build.gradle: 5.006

✅ No secrets or suspicious high-entropy strings found.

Mid-4 beauty heuristic in action — powered by our entropy chats! 😊

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 5.006 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

build.gradle: 5.006

✅ No secrets or suspicious high-entropy strings found.

Mid-4 beauty heuristic in action — powered by our entropy chats! 😊