Replaces the "doesn't" contraction with "does not" to be consistent with similar strings in `WP_Error` messages when a specified term or parent term is missing in `WP_REST_Terms_Controller`.
Props ramiy, ocean90.
Fixes#39176.
Built from https://develop.svn.wordpress.org/trunk@39648
git-svn-id: http://core.svn.wordpress.org/trunk@39588 1a063a9b-81f0-0310-95a4-ce76da25c4cd