Fix milestone deadline and date related problems (#32339)

Use zero instead of 9999-12-31 for deadline
Fix #32291

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

models/migrations/v1_23/v307.go

@@ -0,0 +1,21 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_23 //nolint
+
+import (
+	"code.gitea.io/gitea/modules/timeutil"
+
+	"xorm.io/xorm"
+)
+
+func FixMilestoneNoDueDate(x *xorm.Engine) error {
+	type Milestone struct {
+		DeadlineUnix timeutil.TimeStamp
+	}
+	// Wednesday, December 1, 9999 12:00:00 AM GMT+00:00
+	_, err := x.Table("milestone").Where("deadline_unix > 253399622400").
+		Cols("deadline_unix").
+		Update(&Milestone{DeadlineUnix: 0})
+	return err
+}