[sankaku] fix extracting extended tag categories (#7744)

by sending a proper Referer header
and not one from https://sankaku.app/

gallery_dl/extractor/sankaku.py

@@ -90,7 +90,8 @@ class SankakuExtractor(BooruExtractor):
     def _tags_extended(self, post, page):
         try:
             url = "https://chan.sankakucomplex.com/posts/" + post["id"]
-            page = self.request(url).text
+            headers = {"Referer": url}
+            page = self.request(url, headers=headers).text
         except Exception as exc:
             return self.log.warning(
                 "%s: Failed to extract extended tag categories (%s: %s)",