Release tests need to block non-release PRs

[skitt]

The releases repository has tests to reduce the risk of breakage when changes are made; but these are skipped on release PRs. As a result, the tests can’t be made to block PRs, they need to be disabled for releases.

Instead of skipping the tests entirely, the tests should run without checking anything on release PRs, and the tests should then block PRs.

[github-actions]

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