[SPARK-57692][INFRA] Skip test report when no test results exist

[sarutak]

What changes were proposed in this pull request?

This PR adds a check in test_report.yml to skip the test report publishing step when no test result XML files are found after downloading artifacts.

Why are the changes needed?

When a commit only modifies files in the dev-tools module (e.g., LICENSE-binary), no build or tests are executed. However, the "Report test results" workflow still triggers on the Build workflow's completion and fails with "No test results found!" because there are no test artifacts to report on.

• https://github.com/apache/spark/runs/83376805611
• https://github.com/apache/spark/runs/83376713136
• https://github.com/apache/spark/runs/83376067066

SPARK-55594 (78ab6e2) previously addressed the same "No test results found!" error for the pages.yml case by filtering out that specific workflow path. However, the dev-tools module case was not covered. This PR takes a more general approach by checking for the actual presence of test result files, which handles all cases where tests are legitimately not executed, including any future ones.

Note: The existing pages.yml filter in the job's if condition is intentionally kept. It avoids spinning up the job entirely for a known no-op case, saving runner resources.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Self review. Also, this will be validated by observing that commits which only modify files in the dev-tools module (e.g., LICENSE-binary, README.md, .gitignore) no longer produce a failed "Report test results" check.

Was this patch authored or co-authored using generative AI tooling?

Kiro CLI / Claude

[dongjoon-hyun]

+1, LGTM. Yes, the previous attempt was insufficient. Thank you, @sarutak .

[uros-b]

Thank you for the changes and addressing the comments @sarutak! LGTM