Show exception in cleanup error (#10430)

* Show execption in cleanup error

* Fixed indentation

---------

Co-authored-by: Carl Christian Snethlage <50491877+calixtus@users.noreply.github.com>

Author: Siedlerchr

src/main/java/org/jabref/gui/cleanup/CleanupAction.java

@@ -89,6 +89,7 @@ public void execute() {
 
             BackgroundTask.wrap(() -> cleanup(stateManager.getActiveDatabase().get(), preset))
                           .onSuccess(result -> showResults())
+                          .onFailure(dialogService::showErrorDialogAndWait)
                           .executeWith(taskExecutor);
         });
     }