replace 2-element f-strings with simple '+' concatenations

Python's 'ast' module and its 'NodeVisitor' class
were incredibly helpful in identifying these

gallery_dl/extractor/reddit.py

@@ -223,10 +223,10 @@ class RedditExtractor(Extractor):
                     self.log.debug(src)
             elif url := data.get("dashUrl"):
                 submission["_ytdl_manifest"] = "dash"
-                yield f"ytdl:{url}"
+                yield "ytdl:" + url
             elif url := data.get("hlsUrl"):
                 submission["_ytdl_manifest"] = "hls"
-                yield f"ytdl:{url}"
+                yield "ytdl:" + url
 
     def _extract_video_ytdl(self, submission):
         return "https://www.reddit.com" + submission["permalink"]
@@ -506,7 +506,7 @@ class RedditAPI():
         return "Bearer " + data["access_token"]
 
     def _call(self, endpoint, params):
-        url = f"{self.root}{endpoint}"
+        url = self.root + endpoint
         params["raw_json"] = "1"
 
         while True: