[extractor/youtube:tab] Support shorts-only playlists (#7425)

Fixes https://github.com/yt-dlp/yt-dlp/issues/7424

Authored by: coletdjnz
Co-authored-by: pukkandan <pukkandan.ytdlp@gmail.com>

yt_dlp/extractor/youtube.py

@@ -4898,7 +4898,8 @@ class YoutubeTabBaseInfoExtractor(YoutubeBaseInfoExtractor):
                     'videoRenderer': lambda x: [self._video_entry(x)],
                     'playlistRenderer': lambda x: self._grid_entries({'items': [{'playlistRenderer': x}]}),
                     'channelRenderer': lambda x: self._grid_entries({'items': [{'channelRenderer': x}]}),
-                    'hashtagTileRenderer': lambda x: [self._hashtag_tile_entry(x)]
+                    'hashtagTileRenderer': lambda x: [self._hashtag_tile_entry(x)],
+                    'richGridRenderer': lambda x: self._extract_entries(x, continuation_list),
                 }
                 for key, renderer in isr_content.items():
                     if key not in known_renderers:
@@ -6390,6 +6391,28 @@ class YoutubeTabIE(YoutubeTabBaseInfoExtractor):
             'channel_is_verified': True,
         },
         'playlist_mincount': 10,
+    }, {
+        # Playlist with only shorts, shown as reel renderers
+        # FIXME: future: YouTube currently doesn't give continuation for this,
+        # may do in future.
+        'url': 'https://www.youtube.com/playlist?list=UUxqPAgubo4coVn9Lx1FuKcg',
+        'info_dict': {
+            'id': 'UUxqPAgubo4coVn9Lx1FuKcg',
+            'channel_url': 'https://www.youtube.com/channel/UCxqPAgubo4coVn9Lx1FuKcg',
+            'view_count': int,
+            'uploader_id': '@BangyShorts',
+            'description': '',
+            'uploader_url': 'https://www.youtube.com/@BangyShorts',
+            'channel_id': 'UCxqPAgubo4coVn9Lx1FuKcg',
+            'channel': 'Bangy Shorts',
+            'uploader': 'Bangy Shorts',
+            'tags': [],
+            'availability': 'public',
+            'modified_date': '20230626',
+            'title': 'Uploads from Bangy Shorts',
+        },
+        'playlist_mincount': 100,
+        'expected_warnings': [r'[Uu]navailable videos (are|will be) hidden'],
     }]
 
     @classmethod