Makes corncobs produce seeds (#77944)

## About The Pull Request
This adds a new type of corncob for snapcorn and makes both types
produce their respective seeds when used in a seed extractor or portable
seed extractor.
## Why It's Good For The Game
No more using corncobs on the extractor for the message but not getting
any seeds.

![image](https://github.com/tgstation/tgstation/assets/53197594/15fc4949-37ab-47a6-9195-e3e2a6dcf010)

![image](https://github.com/tgstation/tgstation/assets/53197594/134fe504-9e9c-4ac9-8a67-22e2a097c785)
## Changelog
🆑
fix: fixed corn cobs not making seeds and lying to you in the text box.
/🆑

---------

Co-authored-by: MrMelbert <51863163+MrMelbert@users.noreply.github.com>

code/modules/hydroponics/grown/corn.dm

@@ -36,6 +36,7 @@
 	AddElement(/datum/element/microwavable, /obj/item/food/popcorn)
 
 /obj/item/grown/corncob
+	seed = /obj/item/seeds/corn
 	name = "corn cob"
 	desc = "A reminder of meals gone by."
 	icon_state = "corncob"
@@ -89,5 +90,10 @@
 		user.put_in_hands(S)
 	snap_pops -= 1
 	if(!snap_pops)
-		new /obj/item/grown/corncob(user.loc)
+		new /obj/item/grown/corncob/snap(user.loc)
 		qdel(src)
+
+/obj/item/grown/corncob/snap
+	seed = /obj/item/seeds/corn/snapcorn
+	name = "snap corn cob"
+	desc = "A reminder of pranks gone by."