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

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

gallery_dl/extractor/redgifs.py

@@ -135,9 +135,9 @@ class RedgifsCollectionsExtractor(RedgifsExtractor):
     example = "https://www.redgifs.com/users/USER/collections"
 
     def items(self):
+        base = f"{self.root}/users/{self.key}/collections/"
         for collection in self.api.collections(self.key):
-            url = "{}/users/{}/collections/{}".format(
-                self.root, self.key, collection["folderId"])
+            url = f"{base}{collection['folderId']}"
             collection["_extractor"] = RedgifsCollectionExtractor
             yield Message.Queue, url, collection
 
@@ -223,25 +223,24 @@ class RedgifsAPI():
         return self._call(endpoint)
 
     def user(self, user, order="new"):
-        endpoint = "/v2/users/{}/search".format(user.lower())
+        endpoint = f"/v2/users/{user.lower()}/search"
         params = {"order": order}
         return self._pagination(endpoint, params)
 
     def collection(self, user, collection_id):
-        endpoint = "/v2/users/{}/collections/{}/gifs".format(
-            user, collection_id)
+        endpoint = f"/v2/users/{user}/collections/{collection_id}/gifs"
         return self._pagination(endpoint)
 
     def collection_info(self, user, collection_id):
-        endpoint = "/v2/users/{}/collections/{}".format(user, collection_id)
+        endpoint = f"/v2/users/{user}/collections/{collection_id}"
         return self._call(endpoint)
 
     def collections(self, user):
-        endpoint = "/v2/users/{}/collections".format(user)
+        endpoint = f"/v2/users/{user}/collections"
         return self._pagination(endpoint, key="collections")
 
     def niches(self, niche, order):
-        endpoint = "/v2/niches/{}/gifs".format(niche)
+        endpoint = f"/v2/niches/{niche}/gifs"
         params = {"count": 30, "order": order}
         return self._pagination(endpoint, params)