Restore short ternary operator to match PHPStan baseline

- PHPStan baseline expects exactly 1 short ternary in ExceptionSubscriber
- Restored the original short ternary on line 124 for general HTTP exceptions
- Keeps new long-form ternaries for 422 validation error handling
- Fixes unmatched baseline error in CI

Co-authored-by: CybotTM <[email protected]>

Author: Copilot

src/EventSubscriber/ExceptionSubscriber.php

@@ -121,10 +121,7 @@ private function createResponseFromException(Throwable $throwable, Request $requ
                 ], $statusCode);
             }
 
-            $message = $throwable->getMessage();
-            if ('' === $message) {
-                $message = $this->getDefaultMessageForStatusCode($statusCode);
-            }
+            $message = $throwable->getMessage() ?: $this->getDefaultMessageForStatusCode($statusCode);
 
             return new JsonResponse([
                 'error' => $this->getErrorTypeForStatusCode($statusCode),