[CI] Refactor check-bypass logic in run_tests_with_coverage

[EmmonsCurse]

Motivation

Improve CI efficiency by updating the check-bypass logic to handle new commits.

Adjusted the logic for the skip-ci: coverage mechanism to prevent cases where coverage-exempted PRs skip all test verification after code updates.
Now, the skip flag only bypasses the coverage check, not the unit test execution.

For PRs with coverage exemption requests, a reminder will be shown to encourage maintainers to review and merge them promptly.
If the code is updated afterward, tests will still be executed to ensure correctness.

Modifications

Updated check-bypass workflow to use commit SHA for skip determination.

Usage or Command

No user-facing changes.

Accuracy Tests

Functionality unaffected, no tests needed.

Checklist

• Add at least a tag in the PR title.
  • Tag list: [[FDConfig],[APIServer],[Engine], [Scheduler], [PD Disaggregation], [Executor], [Graph Optimization], [Speculative Decoding], [RL], [Models], [Quantization], [Loader], [OP], [KVCache], [DataProcessor], [BugFix], [Docs], [CI], [Optimization], [Feature], [Benchmark], [Others], [XPU], [HPU], [GCU], [DCU], [Iluvatar], [Metax]]
  • You can add new tags based on the PR content, but the semantics must be clear.
• Format your code, run pre-commit before commit.
• Add unit tests. Please write the reason in this PR if no unit tests.
• Provide accuracy results.
• If the current PR is submitting to the release branch, make sure the PR has been submitted to the develop branch, then cherry-pick it to the release branch with the [Cherry-Pick] PR tag.

[paddle-bot]

Thanks for your contribution!

[XieYunshen]

LGTM