Revisions and improvements to PR workflows

[llxia]

1. Update workflows to reduce the amount of tests that are triggered (should only be a sniff test, not hours of test execution).
2. Check that the Github runners are being set up properly (with up-to-date prereqs, jtreg version, etc).
3. Trigger workflow after pushing changes to a PR

• We limited automatically triggered PR testing to ready_for_review (see: https://github.com/AdoptOpenJDK/openjdk-tests/blob/master/.github/workflows/directoriesFilesChangePR.yml#L4).
• If people do not create a draft, the workflow does not get triggered. The workflow should be triggered after pushing changes to a PR. Maybe we should use synchronize . We should check the gitbub docs.

[patkarns]

Changes are in pull request #2292