Use correct file name in a hook comment.

props wedi.
fixes #30200.

git-svn-id: https://develop.svn.wordpress.org/trunk@30117 602fd350-edb4-49c9-b593-d223f7449a82
Move `term_exists()` tests to their own file.

git-svn-id: https://develop.svn.wordpress.org/trunk@30118 602fd350-edb4-49c9-b593-d223f7449a82