Allow apostrophes in email address during wp-login.php registration.

See #18039 for a related fix when creating users via the Dashboard.

Props tomdxw.
Fixes #34483.
Built from https://develop.svn.wordpress.org/trunk@39544


git-svn-id: https://core.svn.wordpress.org/trunk@39484 1a063a9b-81f0-0310-95a4-ce76da25c4cd