Docs: Add a @since note to wp_mail() about using is_email() for validation.

Follow-up to [48645].

See #52628.

git-svn-id: https://develop.svn.wordpress.org/trunk@50781 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/pluggable.php

@@ -158,6 +158,8 @@ if ( ! function_exists( 'wp_mail' ) ) :
 	 * be set using the {@see 'wp_mail_charset'} filter.
 	 *
 	 * @since 1.2.1
+	 * @since 5.5.0 is_email() is used for email validation,
+	 *              instead of PHPMailer's default validator.
 	 *
 	 * @global PHPMailer\PHPMailer\PHPMailer $phpmailer
 	 *