Code Quality: Correct hook registration type mismatches.

Though `add_action()` and `add_filter()` are functionally equivalent internally, for proper semantics the former should be used on actions and the latter on filters.

Follow-up to [37920], [38046], [53266].

Props apermo.
Fixes #64828.

git-svn-id: https://develop.svn.wordpress.org/trunk@61866 602fd350-edb4-49c9-b593-d223f7449a82