Administration: Improve the error message sent when bulk role change skips the current user.

This changeset clarifies the error message displayed when the current user tries to change their role to one that does not allow managing other users.

Props dpknauss, audrasjb, huzaifaalmesbah, noruzzaman, r1k0.
Fixes #64690.



git-svn-id: https://develop.svn.wordpress.org/trunk@61854 602fd350-edb4-49c9-b593-d223f7449a82