test: ci/merge label with failing build — should still enter merge queue

[cgwalters]

Has ci/fail-build so the tier-1 build job will deliberately fail. The ci/merge label is applied so the full tier-2 suite runs too.

Key test: required-checks should still turn green on the PR (because required-checks-merge is skipped on pull_request events), allowing this PR to enter the merge queue even with the failing heavy job.

In the merge queue the jobs run fresh, so a flaky job gets a clean retry.

[gemini-code-assist]

Code Review

This pull request adds a text file to the test-results/ directory to document a CI test scenario. Feedback suggests moving this file to a more permanent directory like tests/ or ci/ to follow standard conventions and avoid accidental deletion, along with a suggestion for more formal wording.

[gemini-code-assist]

The directory 'test-results/' is conventionally used for ephemeral test output and reports, which are typically excluded from version control. Committing a persistent file here may be confusing or lead to accidental deletion by cleanup scripts. Consider moving this file to a directory intended for test sources or documentation, such as 'tests/' or 'ci/'. Additionally, the description could be more formal and use clearer terminology.

This PR uses the 'ci/merge' label and the 'ci/fail-build' file. The key test is to verify that 'required-checks' passes on the PR, allowing it to enter the merge queue.