Improve gh-pr-checks polling logs and case handling

[qqrm]

Motivation

• Make the gh pr checks polling more robust against transient/variant CLI output and API glitches by avoiding exact-case matching of the temporary "no checks reported" message and by avoiding false positives when gh returns errors or empty output.
• Provide lightweight progress logging so it's clear in runner logs that the action is waiting for checks and how long it has been waiting.

Description

• Updated the composite action .github/actions/gh-pr-checks/action.yml to read checks_output with checks_output="$(gh pr checks "$PR" 2>&1 || true)" and use case-insensitive matching via grep -qi "no checks reported" before deciding to wait.
• Added start-time tracking, periodic [INFO] No checks yet (elapsed=${elapsed}s), waiting... logs, [INFO] Checks detected for PR #$PR on detection, a sleep 4 between polls, and honor the existing MAX_WAIT_SECONDS input to time out.

Testing

• No automated tests were run; this is a CI/action change and should be validated by the next workflow run on GitHub.

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Codex Task