Captain's Spare ID Safe Can Only Hold ID Cards (tgstation#72584)

## About The Pull Request

I've personally seen this strategy play out the exact same way on more
than one occasion in an higher frequency lately (I've never played as
either side, just witnessed it)- and it always just seems to be an abuse
of a skewed in-game mechanic. So, this PR makes it so that you can only
put IDs into the spare ID safe. Nothing else.
## Why It's Good For The Game

I think this balance change is needed because it really sort of ruins
what I like about nuclear operatives, having to run around and stay
fluid for whatever the nuclear operatives could have, not "HAHA WE WILL
PUT IT IN OUR (NEARLY) IMPENETRABLE SAFE THAT THEY WILL NEED TO USE A C4
DIRECTLY ON AND JUST END UP PLAYING BLOONS TOWER DEFENSE SIX AS WE AWAIT
THOSE RED FUCKS TO ARRIVE". I miss when it would be fun to inject it
into a monkey who could crawl around vents, put it in a disposals loop
around the station to keep the nukies on a wild goose chase, or just
holding your ground in the brig and retreating if they batter you down.
It's just a very OP location in a very OP place with lots of warranted
OP armor for it's intended use case, which is not really being followed
by putting the all-important disk in the safe.

It's just very strong overall due to how protected-from-damage the spare
ID safe is, and I don't really like the fact that this is emerging as a
new "meta gameplay" (even used when there aren't any nuclear
operatives), it just sullies the different variety of ways you can
defend yourself against nuclear operatives when there appears to be
**the clear choice**. I don't like that concept where you can have a
strategy so good that you _shouldn't_ do it.

Also, it's an _ID Safe_. Not a disk safe.
## Changelog
:cl:
balance: Due to materials costing a lot more than ever, Nanotrasen's
Spare ID Safe Supplier have cut down on the space inside of the ID Safe,
meaning you can only cram in things as thin as an ID Card.
/:cl:

code/game/objects/items/storage/secure.dm

@@ -208,7 +208,8 @@ MAPPING_DIRECTIONAL_HELPERS(/obj/item/storage/secure/safe, 32)
 	name = "captain's spare ID safe"
 	desc = "In case of emergency, do not break glass. All Captains and Acting Captains are provided with codes to access this safe. \
 It is made out of the same material as the station's Black Box and is designed to resist all conventional weaponry. \
-There appears to be a small amount of surface corrosion. It doesn't look like it could withstand much of an explosion."
+There appears to be a small amount of surface corrosion. It doesn't look like it could withstand much of an explosion.\
+It remains quite flush against the wall, and there only seems to be enough room to fit something as slim as an ID card."
 	can_hack_open = FALSE
 	armor_type = /datum/armor/safe_caps_spare
 	max_integrity = 300
@@ -227,6 +228,7 @@ MAPPING_DIRECTIONAL_HELPERS(/obj/item/storage/secure/safe/caps_spare, 32)
 
 /obj/item/storage/secure/safe/caps_spare/Initialize(mapload)
 	. = ..()
+	atom_storage.set_holdable(can_hold_list = list(/obj/item/card/id))
 	lock_code = SSid_access.spare_id_safe_code
 	lock_set = TRUE
 	atom_storage.locked = TRUE