Added hostile spawn tag to rats, since theyre hostile (#74935)

## About The Pull Request

Added the HOSTILE_SPAWN tag to rats. Otherwise, they can be spawned when
they shouldn't, like during the friendly life chemical reaction

## Why It's Good For The Game

Helps prevent accidental griefing with the friendly life reaction. I've
used the reaction to make fun pets for the station, only for a rat to
spawn and attack a crew mate.

## Changelog

🆑
add: Added hostile spawn tag to rats
/🆑

code/modules/mob/living/basic/vermin/mouse.dm

@@ -268,6 +268,7 @@
 	name = "rat"
 	desc = "They're a nasty, ugly, evil, disease-ridden rodent with anger issues."
 
+	gold_core_spawnable = NO_SPAWN
 	melee_damage_lower = 3
 	melee_damage_upper = 5
 	obj_damage = 5