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/migrations.go

@@ -364,6 +364,7 @@ func prepareMigrationTasks() []*migration {
 		newMigration(304, "Add index for release sha1", v1_23.AddIndexForReleaseSha1),
 		newMigration(305, "Add Repository Licenses", v1_23.AddRepositoryLicenses),
 		newMigration(306, "Add BlockAdminMergeOverride to ProtectedBranch", v1_23.AddBlockAdminMergeOverrideBranchProtection),
+		newMigration(307, "Fix milestone deadline_unix when there is no due date", v1_23.FixMilestoneNoDueDate),
 	}
 	return preparedMigrations
 }