[ie/youtube] Fix n function name extraction for player 3400486c (#10542)

Authored by: bashonly

yt_dlp/extractor/youtube.py

@@ -3131,7 +3131,14 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
 
     def _extract_n_function_name(self, jscode):
         funcname, idx = self._search_regex(
-            r'''(?x)(?:\.get\("n"\)\)&&\(b=|b=String\.fromCharCode\(110\),c=a\.get\(b\)\)&&\(c=)
+            r'''(?x)
+            (?:
+                \.get\("n"\)\)&&\(b=|
+                (?:
+                    b=String\.fromCharCode\(110\)|
+                    ([a-zA-Z0-9$.]+)&&\(b="nn"\[\+\1\]
+                ),c=a\.get\(b\)\)&&\(c=
+            )
             (?P<nfunc>[a-zA-Z0-9$]+)(?:\[(?P<idx>\d+)\])?\([a-zA-Z0-9]\)''',
             jscode, 'Initial JS player n function name', group=('nfunc', 'idx'))
         if not idx: