[sankaku] fix 'tags' metadata (#7155)

rename 'tag_names' to 'tags'

gallery_dl/extractor/sankaku.py

@@ -66,8 +66,7 @@ class SankakuExtractor(BooruExtractor):
     def _prepare(self, post):
         post["created_at"] = post["created_at"]["s"]
         post["date"] = text.parse_timestamp(post["created_at"])
-        post["tags"] = [tag["name"].lower().replace(" ", "_")
-                        for tag in post["tags"] if tag["name"]]
+        post["tags"] = post.pop("tag_names", ())
         post["tag_string"] = " ".join(post["tags"])
         post["_http_validate"] = self._check_expired
 

test/results/sankaku.py

@@ -186,17 +186,10 @@ __tests__ = (
     "#class"   : sankaku.SankakuPostExtractor,
     "#options" : {"tags": True},
 
-    "id"       : "9PMwlDWjXaB",
-    "md5"      : "dc9a3cbfcfee836779bc4f8d5d95c346",
-    "tag_names": "len:106",
+    "id"  : "9PMwlDWjXaB",
+    "md5" : "dc9a3cbfcfee836779bc4f8d5d95c346",
+    "tags": "len:106",
 
-    "tags": [
-        "mahou_shoujo_madoka_magica",
-        "mahou_shoujo_madoka_magica:_hangyaku_no_monogatari",
-        "pixiv",
-        "akemi_homura",
-        "kaname_madoka",
-    ],
     "tags_copyright": [
         "mahou_shoujo_madoka_magica",
         "mahou_shoujo_madoka_magica:_hangyaku_no_monogatari",