Fix incorrect notification commit url (#21479) (#21483)

Backport #21479

For normal commits the notification url was wrong because oldCommitID is
received from the shrinked commits list.

This PR moves the commits list shrinking after the oldCommitID
assignment.

Author: wxiaoguang

services/repository/push.go

@@ -220,10 +220,6 @@ func pushUpdates(optsList []*repo_module.PushUpdateOptions) error {
 					log.Error("updateIssuesCommit: %v", err)
 				}
 
-				if len(commits.Commits) > setting.UI.FeedMaxCommitNum {
-					commits.Commits = commits.Commits[:setting.UI.FeedMaxCommitNum]
-				}
-
 				oldCommitID := opts.OldCommitID
 				if oldCommitID == git.EmptySHA && len(commits.Commits) > 0 {
 					oldCommit, err := gitRepo.GetCommit(commits.Commits[len(commits.Commits)-1].Sha1)
@@ -251,6 +247,10 @@ func pushUpdates(optsList []*repo_module.PushUpdateOptions) error {
 					commits.CompareURL = ""
 				}
 
+				if len(commits.Commits) > setting.UI.FeedMaxCommitNum {
+					commits.Commits = commits.Commits[:setting.UI.FeedMaxCommitNum]
+				}
+
 				notification.NotifyPushCommits(pusher, repo, opts, commits)
 
 				if err = git_model.RemoveDeletedBranchByName(repo.ID, branch); err != nil {