Clean up cache invalidation suspension global in unit tests.

This fixes a test that was introduced in [30073] which was polluting later
tests.

See #21760.
Built from https://develop.svn.wordpress.org/trunk@30112


git-svn-id: http://core.svn.wordpress.org/trunk@30112 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Streamline some `get_terms()` cache tests.

* Split large method into a number of smaller tests.
* Create fewer fixtures.

See #30017.
Built from https://develop.svn.wordpress.org/trunk@30113


git-svn-id: http://core.svn.wordpress.org/trunk@30113 1a063a9b-81f0-0310-95a4-ce76da25c4cd