Fix improper HTMLURL usages in Go code (#22839)

In Go code, HTMLURL should be only used for external systems, like
API/webhook/mail/notification, etc.

If a URL is used by `Redirect` or rendered in a template, it should be a
relative URL (aka `Link()` in Gitea)

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

models/repo/repo.go

@@ -274,7 +274,7 @@ func (repo *Repository) CommitLink(commitID string) (result string) {
 	if commitID == "" || commitID == "0000000000000000000000000000000000000000" {
 		result = ""
 	} else {
-		result = repo.HTMLURL() + "/commit/" + url.PathEscape(commitID)
+		result = repo.Link() + "/commit/" + url.PathEscape(commitID)
 	}
 	return result
 }