Fix missing repository id when migrating release attachments (#36389)

This PR fixes missed repo_id on the migration of attachments to Gitea.
It also provides a doctor check to fix the dirty data on the database.

models/migrations/v1_26/v325.go

@@ -0,0 +1,18 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_26
+
+import (
+	"xorm.io/xorm"
+)
+
+func FixMissedRepoIDWhenMigrateAttachments(x *xorm.Engine) error {
+	_, err := x.Exec("UPDATE `attachment` SET `repo_id` = (SELECT `repo_id` FROM `issue` WHERE `issue`.`id` = `attachment`.`issue_id`) WHERE `issue_id` > 0 AND (`repo_id` IS NULL OR `repo_id` = 0);")
+	if err != nil {
+		return err
+	}
+
+	_, err = x.Exec("UPDATE `attachment` SET `repo_id` = (SELECT `repo_id` FROM `release` WHERE `release`.`id` = `attachment`.`release_id`) WHERE `release_id` > 0 AND (`repo_id` IS NULL OR `repo_id` = 0);")
+	return err
+}