Add return type union to cast_value() method

Use explicit union type (string|bool|int|float|array) instead of
mixed for better type safety and documentation.

Author: jorgefilipecosta

src/wp-includes/abilities/class-wp-settings-abilities.php

@@ -355,9 +355,9 @@ public static function execute_get_settings( $input = array() ): array {
 	 *
 	 * @param mixed  $value The value to cast.
 	 * @param string $type  The registered type (string, boolean, integer, number, array, object).
-	 * @return mixed The cast value.
+	 * @return string|bool|int|float|array The cast value.
 	 */
-	private static function cast_value( $value, string $type ) {
+	private static function cast_value( $value, string $type ): string|bool|int|float|array {
 		switch ( $type ) {
 			case 'boolean':
 				return (bool) $value;