Playlist status: Don't overwrite playlist timestamp with older date

the playlists are sorted by date descending, so currently older playlist (processed last) have older created dates and overwrite newer ones, making that datapoint pretty useless

listenbrainz/webserver/views/status_api.py

@@ -113,6 +113,10 @@ def get_playlists_timestamp():
             return last_updated
         for playlist in playlists:
             source_patch = playlist.additional_metadata["algorithm_metadata"]["source_patch"]
+            if source_patch in last_updated:
+                # playlists are sorted by created date in descending order
+                # don't overwrite the previously set timestamp for that playlist patch
+                continue
             last_updated_ts = int(playlist.last_updated.timestamp())
             last_updated[source_patch] = last_updated_ts
         cache.set(cache_key, last_updated, PLAYLIST_CACHE_TIME)