Docs: Clarify the weekday range in WP_Locale::get_weekday().

Trac ticket: https://core.trac.wordpress.org/ticket/64522
WordPress.org contributor: raulsalvat

Author: rootzero00

src/wp-includes/class-wp-locale.php

@@ -262,7 +262,7 @@ public function init() {
 	 *
 	 * @since 2.1.0
 	 *
-	 * @param int $weekday_number 0 for Sunday through 6 Saturday.
+	 * @param int<0, 6> $weekday_number 0 for Sunday through 6 Saturday.
 	 * @return string Full translated weekday.
 	 */
 	public function get_weekday( $weekday_number ) {