Split migrations folder (#21549)

There are too many files in `models/migrations` folder so that I split
them into sub folders.

models/migrations/v1_12/v126.go

@@ -0,0 +1,25 @@
+// Copyright 2020 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.
+
+package v1_12 //nolint
+
+import (
+	"xorm.io/builder"
+	"xorm.io/xorm"
+)
+
+func FixTopicRepositoryCount(x *xorm.Engine) error {
+	_, err := x.Exec(builder.Delete(builder.NotIn("`repo_id`", builder.Select("`id`").From("`repository`"))).From("`repo_topic`"))
+	if err != nil {
+		return err
+	}
+
+	_, err = x.Exec(builder.Update(
+		builder.Eq{
+			"`repo_count`": builder.Select("count(*)").From("`repo_topic`").Where(builder.Eq{
+				"`repo_topic`.`topic_id`": builder.Expr("`topic`.`id`"),
+			}),
+		}).From("`topic`").Where(builder.Eq{"'1'": "1"}))
+	return err
+}