Makes the Clown Stamp give out clown cells (tgstation#83585)

## About The Pull Request

This PR makes it so swabbing the clown's stamp also gives clown cells
for Cytology.

## Why It's Good For The Game
Right now for these cell lines you either need to swab the clown's
shoes, clothes or mask - items that many clowns won't be too happy to
part with, even if for a few seconds. Furthermore it means you only get
3 tries to get the cell line you want, alongside having a chance of
having all of the cell lines rather than just two (making the process a
lot more harder if i does happen).

Letting the stamp give out cells both makes getting a single petri dish
faster ("Clown give me the stamp" "K") but also means if you're going
for one specific cell line you have more chances to get it, making the
whole process of getting experimental clowns faster and more reliable
overall.

## Changelog
:cl:
qol: Swabbing the clown's stamp also gives clown cells.
:cl:

code/modules/paperwork/stamps.dm

@@ -88,6 +88,11 @@
 	icon_state = "stamp-clown"
 	dye_color = DYE_CLOWN
 
+/obj/item/stamp/clown/Initialize(mapload)
+	. = ..()
+
+	AddElement(/datum/element/swabable, CELL_LINE_TABLE_CLOWN, CELL_VIRUS_TABLE_GENERIC, rand(2,3), 0)
+
 /obj/item/stamp/mime
 	name = "mime's rubber stamp"
 	icon_state = "stamp-mime"