Fixes brimdust overlay on wide mobs (#96325)

## About The Pull Request

Lack of KEEP_TOGETHER on some mobs (unlike objects and blood overlays,
we operate under the assumption that all mobs have KEEP_TOGETHER and
thus all of our code is designed to support it) caused brimdust overlay
to leak through onto other objects

## Changelog
🆑
fix: Fixed brimdust overlay on wide mobs leaking onto other objects
/🆑

code/modules/mining/equipment/monster_organs/brimdust_sac.dm

@@ -169,6 +169,7 @@
 	dust_overlay.alpha = stacks * BRIMDUST_ALPHA_PER_STACK
 	dust_overlay.color = COLOR_RED_LIGHT
 	dust_overlay.blend_mode = BLEND_INSET_OVERLAY
+	ADD_KEEP_TOGETHER(owner, REF(src))
 	owner.add_overlay(dust_overlay)
 	var/obj/effect/holder = owner.add_shared_particles(/particles/brimdust, "brimdust_coating-[owner.base_pixel_w]")
 	holder.pixel_w = -owner.base_pixel_w
@@ -178,6 +179,7 @@
 /datum/status_effect/stacking/brimdust_coating/on_remove()
 	. = ..()
 	owner.cut_overlay(dust_overlay)
+	REMOVE_KEEP_TOGETHER(owner, REF(src))
 	owner.remove_shared_particles("brimdust_coating-[owner.base_pixel_w]")
 	UnregisterSignal(owner, list(COMSIG_MOB_APPLY_DAMAGE, COMSIG_COMPONENT_CLEAN_ACT))