ICU-22721 Simplify wait-for-checks match logic

[echeran]

Applying reviewer changes from #3055

Also, if CI for the merge commit for #3055 all looks good (in particular, the wait for checks job), then we might be ready to configure the repo settings' branch protection rules and add enforce-all-checks as a required check.

Checklist

• [X] Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22721
• [X] Required: The PR title must be prefixed with a JIRA Issue number.
• [X] Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• [X] Required: Each commit message must be prefixed with a JIRA Issue number.
• [X] Issue accepted (done by Technical Committee after discussion)
• [ ] Tests included, if applicable
• [X] API docs and/or User Guide docs changed or added, if applicable