Fix spelling mistake in [p]slash sync error (Cog-Creators#6285)

redbot/core/core_commands.py

@@ -2377,7 +2377,7 @@ async def slash_sync_error(self, ctx: commands.Context, error: commands.CommandE
         await ctx.send(
             _(
                 "You seem to be attempting to sync after recently syncing. Discord does not like it "
-                "when bots sync more often than neccecary, so this command has a cooldown. You "
+                "when bots sync more often than necessary, so this command has a cooldown. You "
                 "should enable/disable all commands you want to change first, and run this command "
                 "one time only after all changes have been made. "
             )