Site Health: Recognize `define( 'WP_AUTO_UPDATE_CORE', 'minor' )` as an acceptable value.

Previously, it was only incidentally recognized as valid due to a loose comparison with `true`.

With the strict comparison added to `WP_Site_Health_Auto_Updates::test_constants()`, this was no longer the case.

Follow-up to [47841].

Props sterndata, mukesh27, avixansa, desrosj, SergeyBiryukov.
Merges [48792] to the 5.5 branch.
Fixes #50912.
Built from https://develop.svn.wordpress.org/branches/5.5@48804


git-svn-id: https://core.svn.wordpress.org/branches/5.5@48566 1a063a9b-81f0-0310-95a4-ce76da25c4cd