This removes the need to manually call `$this->skipWithMultisite()` and `$this->skipWithoutMultisite()` from within the test when the test only runs without Multisite or only runs on Multisite, respectively.
Props jdgrimes for the suggestion.
Fixes#40531
git-svn-id: https://develop.svn.wordpress.org/trunk@40564 602fd350-edb4-49c9-b593-d223f7449a82