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

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

[echeran]

Merging this now. This just simplifies the workflow, but won't affect the ability to merge PRs in any way since the workflow is not a required check. So far, the workflow has run 2 times on main, once successfully, and failed once because 2 other jobs were cancelled.

We can see how the workflow performs after merging this PR, and all looks good after some time, we can consider finally adding the workflow's job as a required check to reestablish that all CI jobs are effectively required.