refactor: prepare to decouple the "model migration" package and "models" package (#38533)

Migrations should never use model structs directly, because the model
structs can be different in different releases. e.g. if one migration uses
"User" model, it works in the early releases, then one day, when the
User model changes, the migration breaks because it will use the
new (incorrect) User model, it should only use the old User model.

The same to "modules/structs".

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>

modelmigration/v1_23/v304_test.go

@@ -0,0 +1,40 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_23
+
+import (
+	"testing"
+
+	"gitea.dev/modelmigration/migrationtest"
+	"gitea.dev/modules/timeutil"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_AddIndexForReleaseSha1(t *testing.T) {
+	type Release struct {
+		ID               int64  `xorm:"pk autoincr"`
+		RepoID           int64  `xorm:"INDEX UNIQUE(n)"`
+		PublisherID      int64  `xorm:"INDEX"`
+		TagName          string `xorm:"INDEX UNIQUE(n)"`
+		OriginalAuthor   string
+		OriginalAuthorID int64 `xorm:"index"`
+		LowerTagName     string
+		Target           string
+		Title            string
+		Sha1             string `xorm:"VARCHAR(64)"`
+		NumCommits       int64
+		Note             string             `xorm:"TEXT"`
+		IsDraft          bool               `xorm:"NOT NULL DEFAULT false"`
+		IsPrerelease     bool               `xorm:"NOT NULL DEFAULT false"`
+		IsTag            bool               `xorm:"NOT NULL DEFAULT false"` // will be true only if the record is a tag and has no related releases
+		CreatedUnix      timeutil.TimeStamp `xorm:"INDEX"`
+	}
+
+	// Prepare and load the testing database
+	x, deferable := migrationtest.PrepareTestEnv(t, 0, new(Release))
+	defer deferable()
+
+	assert.NoError(t, AddIndexForReleaseSha1(x))
+}