gives small pistol mag pouch a reason to exist (#6374)

# About the pull request
small pistol mag pouch now has 4 slots

# Explain why it's good for the game
small mag pouch was identical to small pistol mag pouch but you could
also carry rifle mags in it, so there was literally no reason for small
pistol mag pouch to exist - you could always grab rifle mag pouch and
have more utility

# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

wow

![image](https://github.com/cmss13-devs/cmss13/assets/44546836/d54c9879-664a-4e02-ab69-7ee83670a655)


</details>


# Changelog
:cl:
balance: Pistol mag pouch now has 4 slots instead of 3.
/:cl:

yep... balance tag....

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

@@ -425,7 +425,7 @@
 	desc = "It can carry pistol magazines and revolver speedloaders."
 	max_w_class = SIZE_SMALL
 	icon_state = "pistol_mag"
-	storage_slots = 3
+	storage_slots = 4
 
 	can_hold = list(
 		/obj/item/ammo_magazine/pistol,