Add test for ExtendCommentTreePathLength migration and fix bugs (#35791)

Co-authored-by: Mithilesh Gupta <guptamithilesh@protonmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

models/migrations/v1_26/main_test.go

@@ -0,0 +1,14 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_26
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/migrations/base"
+)
+
+func TestMain(m *testing.M) {
+	base.MainTest(m)
+}