[MINOR][CI] Retry Maven test-compile on transient repository download errors

[Baunsgaard]

CI jobs intermittently fail at startup when Maven Central returns a transient error (e.g. HTTP 403 while resolving the Apache parent POM), which is unrelated to the code under test. Retry test-compile once after a short pause when the failure is a "Could not transfer artifact" download error, while genuine compilation and test failures still fail fast.

Also point the test action at the entrypoint script in the mounted workspace so changes to docker/entrypoint.sh take effect immediately without rebuilding and republishing apache/systemds:testing-latest.

Failing job that motivated this change:
https://github.com/apache/systemds/actions/runs/27167144065/job/80197161169

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.40%. Comparing base (ae9a59c) to head (4ede53a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2486      +/-   ##
============================================
- Coverage     71.41%   71.40%   -0.02%     
  Complexity    48774    48774              
============================================
  Files          1571     1571              
  Lines        188912   188912              
  Branches      37067    37067              
============================================
- Hits         134917   134895      -22     
- Misses        43544    43553       +9     
- Partials      10451    10464      +13     

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