[youtube] Improve signature cipher extraction (closes #25188)

youtube_dl/extractor/youtube.py

@@ -1966,7 +1966,7 @@ def _extract_filesize(media_url):
                 url = url_or_none(fmt.get('url'))
 
                 if not url:
-                    cipher = fmt.get('cipher')
+                    cipher = fmt.get('cipher') or fmt.get('signatureCipher')
                     if not cipher:
                         continue
                     url_data = compat_parse_qs(cipher)