ci: optimize rerun workflow and add macOS RocksDB coverage

[contrueCT]

Purpose of the PR

Optimize the Rerun CI workflow so it only starts the rerun decision job when an upstream CI workflow actually fails.

Previously, the rerun workflow also ran for non-failure conclusions and then skipped inside the shell script, which created unnecessary workflow runs.

Main Changes

• Add a job-level condition to decide-rerun-action:
  • only run when github.event.workflow_run.conclusion == 'failure'
• Remove the redundant CONCLUSION shell variable and non-failure branch handling
• Keep the existing rerun behavior unchanged for supported events:
  • push
  • pull_request
• Keep the existing retry limit, delay, permissions, and gh run rerun --failed behavior unchanged

Verifying these changes

• Confirmed the change only affects .github/workflows/rerun-ci.yml

• Trivial rework / code cleanup without any test coverage. (No Need)
• Already covered by existing tests, such as (please modify tests here).
• Need tests and can be verified as follows:
  • Ran git diff --check -- .github/workflows/rerun-ci.yml

Does this PR potentially affect the following parts?

• Dependencies (add/update license info & regenerate_known_dependencies.sh)
• Modify configurations
• The public API
• Other affects (typed here)
• Nope

Documentation Status

• Doc - TODO
• Doc - Done
• Doc - No Need