[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 ae463c7c559e02975ce5e758d8780def978eebee)
(cherry picked from commit bf48f02a86d6a193417f13a77031b8207a173dca)
(cherry picked from commit 10c3f102fa9135de37e9f73137ae5a9cf7072635)
(cherry picked from commit 828b4cc10cd0fc7e2540fe75e88b6ebf978c5c84)
(cherry picked from commit 6427fa65b641a32ead53779e3e7bda97704567df)
(cherry picked from commit 5b7a43c43fed0eb39e84edd652a699461f14fbbb)
(cherry picked from commit 4eef0fce72894fba2a8a138836421588f96f1087)
(cherry picked from commit a46192a4a6cffa1122ffc0c4781ba93c3067b05d)

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