[rule34us] prioritize 'video.rule34.us' for video downloads (#6582)

https://github.com/mikf/gallery-dl/issues/6582#issuecomment-2999111612

gallery_dl/extractor/rule34us.py

@@ -40,7 +40,8 @@ class Rule34usExtractor(BooruExtractor):
 
         url = post["file_url"]
         if "//video-cdn1." in url:
-            post["_fallback"] = (url.replace("//video-cdn1.", "//video."),)
+            post["file_url"] = url.replace("//video-cdn1.", "//video.")
+            post["_fallback"] = (url,)
         post["md5"] = url.rpartition("/")[2].partition(".")[0]
 
         tags = collections.defaultdict(list)