Fix migration v96 to keep issue attachments (#8435)

* Fix migration v96 to keep issue attachments

* Fix == operator

models/migrations/v96.go

@@ -27,7 +27,7 @@ func deleteOrphanedAttachments(x *xorm.Engine) error {
 	defer sess.Close()
 
 	err := sess.BufferSize(setting.Database.IterateBufferSize).
-		Where("`comment_id` = 0 and (`release_id` = 0 or `release_id` not in (select `id` from `release`))").Cols("uuid").
+		Where("`issue_id` = 0 and (`release_id` = 0 or `release_id` not in (select `id` from `release`))").Cols("uuid").
 		Iterate(new(Attachment),
 			func(idx int, bean interface{}) error {
 				attachment := bean.(*Attachment)