Fix replies in dms not being sent (modmail-dev#3239)

* Fix replies not being sent

* Use a list instead of a set

---------

Co-authored-by: Taku <45324516+Taaku18@users.noreply.github.com>

bot.py

@@ -888,7 +888,7 @@ async def process_dm_modmail(self, message: discord.Message) -> None:
             return
         sent_emoji, blocked_emoji = await self.retrieve_emoji()
 
-        if message.type != discord.MessageType.default:
+        if message.type not in [discord.MessageType.default, discord.MessageType.reply]:
             return
 
         thread = await self.threads.find(recipient=message.author)