REST API: Fix permissions error message in post statuses controller.

The permissions error message when a request tries to fetch post statuses unauthenticated is incorrect. It was a copy/paste from elsewhere, as indicated by the use of "in this post type" where this is no post type referenced.

Props schlessera.
Fixes #42303.
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git-svn-id: https://core.svn.wordpress.org/trunk@42185 1a063a9b-81f0-0310-95a4-ce76da25c4cd