OPRUN-3569 was not sufficient in fixing the issue once "shift-left" caused sync PRs to be delayed in merging. We need to use branch-protection and re-run the check-sync-pr-valid job pre-merge.

This will require us to move the check-sync-pr-valid CI job out from underneath the e2e and into it's own test. And then that test will need to be run pre-merge by updating (adding) branch-protection to the _prowconfig.yaml.

Sync PRs generated by the olm v1 bumper have the kind/sync label added as of https://github.com/openshift/operator-framework-tooling/pull/53 .

Add a test to the olm v1 repos for PRs with the sync label to verify that no new commits have landed on the base branch since the PR was created, so no commits already on the base branch get dropped by the sync PR.

See https://redhat-internal.slack.com/archives/C06KP34REFJ/p1727700258066159 for context.