Show commit history for closed/merged PRs (go-gitea#24238)

Close go-gitea#24237

Before:

<details>


![image](https://user-images.githubusercontent.com/2114189/233424875-a69c6dad-df4a-483e-b796-36c6459af2d6.png)

</details>

After:


![image](https://user-images.githubusercontent.com/2114189/233424712-60a296de-017b-49a8-89b2-5925ff452646.png)

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

routers/web/repo/issue.go

@@ -1627,8 +1627,10 @@ func ViewIssue(ctx *context.Context) {
 			comment.Type == issues_model.CommentTypeStopTracking {
 			// drop error since times could be pruned from DB..
 			_ = comment.LoadTime()
-		} else if comment.Type == issues_model.CommentTypeClose {
-			// record ID of latest closed comment.
+		}
+
+		if comment.Type == issues_model.CommentTypeClose || comment.Type == issues_model.CommentTypeMergePull {
+			// record ID of the latest closed/merged comment.
 			// if PR is closed, the comments whose type is CommentTypePullRequestPush(29) after latestCloseCommentID won't be rendered.
 			latestCloseCommentID = comment.ID
 		}