[MIRROR] Fixes birdshots cannonballs not spawning by replacing the cannonballs with a stack [MDB IGNORE] (#22546)

* Fixes birdshots cannonballs not spawning by replacing the cannonballs with a stack (#76839)

## About The Pull Request

pretty much just as the Title says, birdshot used the
obj/projectile/bullet/cannonball path instead of having its own stack of
4 cannonballs, this made it so that it couldn't load the cannonballs as
bullet types don't load as actual items to use.

i have added a 4 stack of cannonballs to the obj/item/stack/cannonball
tree so that way they can get slotted in birdshot to replace 'em, also
for use later by whomever else wants a smaller amount of cannonballs as
the only other amount for regular cannonballs is 14 as used by the
skeletal pirate ship.

## Why It's Good For The Game

with birdshots intention to have originally been overrun by pirates i
assume it was meant to actually spawn because the cannon and gunpowder
barrels also spawn for usage, but the cannonballs themselves didn't.
allows players to find 'em in the area in maints they're supposed to be
found in so you can get up to some hijinks as i assume the creator
intended for all you maint dwellers.

## Changelog

🆑

fix: replaces the unspawnable cannonballs in birdshot maintenance with a
stack so that the 4 cannonballs properly spawn, make sure to point them
away from medical!

/🆑

* Fixes birdshots cannonballs not spawning by replacing the cannonballs with a stack

* Update birdshot.dmm

---------

Co-authored-by: Donglesplonge <120208006+Donglesplonge@users.noreply.github.com>
Co-authored-by: Giz <vinylspiders@gmail.com>

code/game/objects/structures/cannons/cannonballs.dm

@@ -22,6 +22,9 @@
 /obj/item/stack/cannonball/fourteen
 	amount = 14
 
+/obj/item/stack/cannonball/four
+	amount = 4
+
 /obj/item/stack/cannonball/shellball
 	name = "explosive shellballs"
 	singular_name = "explosive shellball"