update extractor test results

- certain posts on Instagram now return
  https://static.cdninstagram.com/rsrc.php/null.jpg
  for public users
- MangaDex is deploying its new MangaDex@Home network similar to
  exhentai's Hentai@Home
- realbooru has a new site layout, but the underlying booru API still
  works like before

gallery_dl/extractor/8muses.py

@@ -53,7 +53,7 @@ class _8musesAlbumExtractor(Extractor):
                 "private": False,
             },
         }),
-        ("https://www.8muses.com/comics/album/Fakku-Comics/7?sort=az", {
+        ("https://www.8muses.com/comics/album/Fakku-Comics/8?sort=az", {
             "count": ">= 70",
             "keyword": {"name": r"re:^[R-Zr-z]"},
         }),