fix(utils): make invalid time format message for sto ephemeral

Co-authored-by: sourcery-ai[bot] <58596630+sourcery-ai[bot]@users.noreply.github.com>

Author: anemoijereja-eden

tux/cogs/utility/self_timeout.py

@@ -47,7 +47,7 @@ async def self_timeout(self, ctx: commands.Context[Tux], duration: str, *, reaso
         duration_readable = seconds_to_human_readable(duration_seconds)
 
         if duration_seconds == 0:
-            await ctx.reply("Error! Invalid time format")
+            await ctx.reply("Error! Invalid time format", ephemeral=True)
             return
 
         if duration_seconds > 604800: