RATIS-2289. Coverage is 0% due to no execution data files provided

[adoroszlai]

What changes were proposed in this pull request?

Calculated coverage is 0% because input files are missing.

[WARN] No execution data files provided.
[INFO] Writing execution data to /home/runner/work/ratis/ratis/dev-support/checks/../../target/coverage/jacoco-all.exec.
[INFO] Loading execution data file /home/runner/work/ratis/ratis/dev-support/checks/../../target/coverage/jacoco-all.exec.
[INFO] Analyzing 694 classes.

https://github.com/apache/ratis/actions/runs/14887012940/job/41810202866#step:7:1977

The problem is re-definition of WITH_COVERAGE variable in unit job. Originally with-coverage was supposed to be a workflow input, but it was removed.

This change:

• removes the leftover definition
• defines global WITH_COVERAGE depending on whether the workflow is triggered by push or pull_reqest
• enables coverage in forks (to exercise coverage.sh and allow checking coverage results before merging to apache/ratis)
• but still skips sonar.sh in forks (since token required for uploading to Sonar Qube is only available in apache/ratis)

https://issues.apache.org/jira/browse/RATIS-2289

How was this patch tested?

[INFO] Loading execution data file /home/runner/work/ratis/ratis/target/artifacts/unit-flaky/jacoco-combined.exec.
[INFO] Loading execution data file /home/runner/work/ratis/ratis/target/artifacts/unit-misc/jacoco-combined.exec.
[INFO] Loading execution data file /home/runner/work/ratis/ratis/target/artifacts/unit-server/jacoco-combined.exec.
[INFO] Loading execution data file /home/runner/work/ratis/ratis/target/artifacts/unit-grpc/jacoco-combined.exec.
[INFO] Writing execution data to /home/runner/work/ratis/ratis/dev-support/checks/../../target/coverage/jacoco-all.exec.
[INFO] Loading execution data file /home/runner/work/ratis/ratis/dev-support/checks/../../target/coverage/jacoco-all.exec.
[INFO] Analyzing 694 classes.

https://github.com/adoroszlai/ratis/actions/runs/14913776473/job/41895151947#step:7:1967

Downloaded coverage.zip and verified coverage is > 0% in all/index.html.

[szetszwo]

+1 the change looks good.

Checked the report. It did have a lot of coverage information.

[adoroszlai]

Thanks @szetszwo for the review.