[commands] Revert on_error when cog is ejected for HelpCommand

discord/ext/commands/help.py

@@ -294,6 +294,9 @@ class _HelpCommandImpl(Command):
         cog.walk_commands = cog.walk_commands.__wrapped__
         self.cog = None
 
+        # Revert `on_error` to use the original one in case of race conditions
+        self.on_error = self._injected.on_help_command_error
+
 
 class HelpCommand:
     r"""The base implementation for help command formatting.