Remove arrow function for backwards compatibility

Author: michaelw85

tests/phpunit/tests/shortcode.php

@@ -447,7 +447,13 @@ public function data_strip_shortcodes() {
 	 * @ticket 26649
 	 */
 	public function test_escaped_shortcode_should_not_execute() {
-		add_shortcode( 'example', fn () => 'foo' );
+		add_shortcode(
+			'example',
+			function () {
+				return 'foo';
+			}
+		);
+
 		$this->assertSame( '[example]', do_shortcode( strip_shortcodes( '[[example]]' ) ) );
 	}