Fix SPDX-License-Identifier

Author: harryzcy

modules/migration/null_uploader.go

@@ -1,6 +1,5 @@
-// Copyright 2022 The Gitea Authors. All rights reserved.
-// Use of this source code is governed by a MIT-style
-// license that can be found in the LICENSE file.
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
 
 package migration