Update ExpressionResultTest.php

Author: staabm

tests/PHPStan/Analyser/ExpressionResultTest.php

@@ -85,6 +85,10 @@ public static function dataIsAlwaysTerminating(): array
 				'(fn() => exit())();', // immediately invoked function expression
 				true,
 			],
+			[
+				'register_shutdown_function(fn() => exit());',
+				false,
+			],
 			[
 				'@exit();',
 				true,