Blocks: Add unit test coverage for Patterns registry.
Prior to this changeset, we did not seem to have any unit test coverage for the Patterns registry (WP_Block_Patterns_Registry).
With Block Hooks logic recently added ([56649]), it is particularly advisable to add some unit tests to the get_registered() and get_all_registered() methods to guard hooked block insertion against regressions.
Fixes #59476.