Fixes summon guns / magic from the secrets menu (#72294)

## About The Pull Request

The proc takes a mob, not a client. `holder`'s a client. 

This is fine if it ends up being `null` for some reason

It's also completely viable to just not pass a mob and keep it `null`,
so that's option B

## Why It's Good For The Game

I could've sworn this worked when I tested it last but 🤷 

## Changelog

🆑 Melbert
fix: Secrets menu Summon Guns / Summon Magic work again.
/🆑

Co-authored-by: Fikou <23585223+Fikou@users.noreply.github.com>

code/modules/admin/verbs/secrets.dm

@@ -277,7 +277,7 @@ GLOBAL_DATUM(everyone_a_traitor, /datum/everyone_is_a_traitor_controller)
 				if("All Antags!")
 					survivor_probability = 100
 
-			summon_guns(holder, survivor_probability)
+			summon_guns(holder.mob, survivor_probability)
 
 		if("magic")
 			if(!is_funmin)
@@ -290,7 +290,7 @@ GLOBAL_DATUM(everyone_a_traitor, /datum/everyone_is_a_traitor_controller)
 				if("All Antags!")
 					survivor_probability = 100
 
-			summon_magic(holder, survivor_probability)
+			summon_magic(holder.mob, survivor_probability)
 
 		if("towerOfBabel")
 			if(!is_funmin)