[commands] Fix Context.send_help to work with the copied HelpCommand

discord/ext/commands/context.py

@@ -261,6 +261,8 @@ class Context(discord.abc.Messageable):
         if cmd is None:
             return None
 
+        cmd = cmd.copy()
+        cmd.context = self
         if len(args) == 0:
             await cmd.prepare_help_command(self, None)
             mapping = cmd.get_bot_mapping()