Commit-Dropdown: Show Author of commit if available (#30272)

As in commits page we show the author of the commit in the commits
dropdown and not the committer.

Commits Page:
![Screenshot from 2024-04-03
22-34-41](https://github.com/go-gitea/gitea/assets/1135157/1c7c5c19-6d0a-4176-8a87-7bca6a0c6dc8)

and the same contents in our dropdown:

![image](https://github.com/go-gitea/gitea/assets/1135157/aa094af2-c369-47ac-9c27-ca208d1d03f0)


fixes #29588

services/pull/pull.go

@@ -989,12 +989,12 @@ func GetPullCommits(ctx *gitea_context.Context, issue *issues_model.Issue) ([]Co
 	for _, commit := range prInfo.Commits {
 		var committerOrAuthorName string
 		var commitTime time.Time
-		if commit.Committer != nil {
-			committerOrAuthorName = commit.Committer.Name
-			commitTime = commit.Committer.When
-		} else {
+		if commit.Author != nil {
 			committerOrAuthorName = commit.Author.Name
 			commitTime = commit.Author.When
+		} else {
+			committerOrAuthorName = commit.Committer.Name
+			commitTime = commit.Committer.When
 		}
 
 		commits = append(commits, CommitInfo{