replace old %-formatted and .format(…) strings with f-strings (#7671)

mostly using flynt
https://github.com/ikamensh/flynt

gallery_dl/extractor/sankaku.py

@@ -201,7 +201,7 @@ class SankakuBooksExtractor(SankakuExtractor):
         params = {"tags": self.tags, "pool_type": "0"}
         for pool in self.api.pools_keyset(params):
             pool["_extractor"] = SankakuPoolExtractor
-            url = "https://sankaku.app/books/{}".format(pool["id"])
+            url = f"https://sankaku.app/books/{pool['id']}"
             yield Message.Queue, url, pool
 
 
@@ -225,10 +225,10 @@ class SankakuAPI():
 
     def notes(self, post_id):
         params = {"lang": "en"}
-        return self._call("/posts/{}/notes".format(post_id), params)
+        return self._call(f"/posts/{post_id}/notes", params)
 
     def tags(self, post_id):
-        endpoint = "/posts/{}/tags".format(post_id)
+        endpoint = f"/posts/{post_id}/tags"
         params = {
             "lang" : "en",
             "page" : 1,