fix some unintentional DNR bugs (#4769)

## About The Pull Request

Changeling Zombie and Medical Revival techniques should no longer bypass
DNR

a future PR should be made to make changeling zombies offer to ghosts,
when the zombie dies the mob is fully finished
## Why It's Good For The Game

bug fix

## Proof Of Testing
<details>
<summary>Screenshots/Videos</summary>

</details>

## Changelog
🆑
fix: changelings can no longer make zombies out of DNR victims
/🆑

code/modules/mob/living/living.dm

@@ -1075,6 +1075,10 @@
 /mob/living/proc/can_be_revived()
 	if(health <= HEALTH_THRESHOLD_DEAD)
 		return FALSE
+		// BUBBER EDIT BEGIN - DNR FAILS REVIVE CHECK
+	if(HAS_TRAIT(src, TRAIT_DNR))
+		return FALSE
+		// BUBBER EDIT END
 	return TRUE
 
 /mob/living/proc/update_damage_overlays()