Bugfix: add an error message level.

This way the error coming from the exception is actually displayed.

(cherry picked from commit 456afe6)

Author: eldering

webapp/src/Controller/Jury/ImportExportController.php

@@ -188,7 +188,7 @@ public function indexAction(Request $request): Response
                     return $this->redirectToRoute('jury_problems');
                 }
             } catch (Exception $e) {
-                $allMessages[] = $e->getMessage();
+                $allMessages['danger'][] = $e->getMessage();
             } finally {
                 if (isset($zip)) {
                     $zip->close();