[GITEA] Skip unsupported code comment

- If there's a code comment that's received during the migration that
contains no diffhunk, skip it. This either means it was commenting on
old diffhunk or it's just a general codecomment. Forgejo supports
neither of such type of code comment.
- Resolves https://codeberg.org/forgejo/forgejo/issues/1407

(cherry picked from commit ae463c7c55)
(cherry picked from commit bf48f02a86)
(cherry picked from commit 10c3f102fa)
(cherry picked from commit 828b4cc10c)
(cherry picked from commit 6427fa65b6)
(cherry picked from commit 5b7a43c43f)
(cherry picked from commit 49eb256648)

services/migrations/gitea_uploader.go

@@ -859,6 +859,11 @@ func (g *GiteaLocalUploader) CreateReviews(reviews ...*base.Review) error {
 		}
 
 		for _, comment := range review.Comments {
+			// Skip code comment if it doesn't have a diff it is commeting on.
+			if comment.DiffHunk == "" {
+				continue
+			}
+
 			line := comment.Line
 			if line != 0 {
 				comment.Position = 1