Fix #235

Use double quote instead of backtick in migrations, because they get executed through shell.

federatedgroups/appinfo/Migrations/Version20230823171700.php

@@ -41,7 +41,7 @@ public function changeSchema(Schema $schema, array $options)
 
 			$fg_group_user_table->addUniqueIndex(
 				['gid', 'uid'],
-				`{$prefix}uc_fg_group_user`
+				"{$prefix}uc_fg_group_user"
 			);
         }
     }