`create_function()` has been deprecated in PHP >= 7.2 and removed in PHP 8.
The only instance left in core was used in a test that was being skipped on PHP >= 7.2. This allows the test to run again.
Follow-up to [41722], [41730].
Props jrf.
Fixes#50899.
git-svn-id: https://develop.svn.wordpress.org/trunk@48790 602fd350-edb4-49c9-b593-d223f7449a82