When a `PUT` request is performed to update a user, a `rest_user_invalid_email` error is incorrectly being returned when the email exists with different letter casing, even if it belongs to the user being updated. `email_exists()` performs a case insensitive lookup, but the conditional statement following that lookup was performing a strict comparison between the new email and the user’s current email.
This changes that comparison to instead compare the user ID returned by `email_exists()` with the user ID being updated. This more closely matches the logic used in `edit_user()` and allows a user to change the letter casing of their email.
Props fuchsws, rachelbaker, desrosj.
Fixes#44672.
git-svn-id: https://develop.svn.wordpress.org/trunk@44641 602fd350-edb4-49c9-b593-d223f7449a82
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