Users: Add extra checking to wp_new_user_notification().

Prevent a notification from being sent when an unrecognised value is passed in the `$notify` parameter.

Props cthreelabs, 360zen.
Fixes #44293.



git-svn-id: https://develop.svn.wordpress.org/trunk@44611 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/user.php

@@ -1169,6 +1169,11 @@ class Tests_User extends WP_UnitTestCase {
 				true,
 				true,
 			),
+			array(
+				'THIS IS NOT A SUPPORTED NOTIFICATION TYPE',
+				false,
+				false,
+			),
 		);
 	}