Site Health: Fix some typos in the test for plugin and theme auto-updates.

Follow-up to [48548], [48558], [48559].

See #50662.
Built from https://develop.svn.wordpress.org/trunk@48560


git-svn-id: https://core.svn.wordpress.org/trunk@48322 1a063a9b-81f0-0310-95a4-ce76da25c4cd