Administration: Use sentence case for "Mark as spam" bulk action links for...

Administration: Use sentence case for "Mark as spam" bulk action links for sites and users, for consistency with comments.

Follow-up to [48352].

See #40244.
Built from https://develop.svn.wordpress.org/trunk@48595


git-svn-id: https://core.svn.wordpress.org/trunk@48357 1a063a9b-81f0-0310-95a4-ce76da25c4cd