Fix incorrect pull request counter (#35819)

Fix #35781, #27472

The PR will not correct the wrong numbers automatically. 

There is a cron task `check_repo_stats` which will be run when Gitea
start or midnight. It will correct the numbers.

models/issues/milestone.go

@@ -181,6 +181,7 @@ func updateMilestone(ctx context.Context, m *Milestone) error {
 func UpdateMilestoneCounters(ctx context.Context, id int64) error {
 	e := db.GetEngine(ctx)
 	_, err := e.ID(id).
+		Cols("num_issues", "num_closed_issues").
 		SetExpr("num_issues", builder.Select("count(*)").From("issue").Where(
 			builder.Eq{"milestone_id": id},
 		)).