Gives a unique sprite to envyknife (tgstation#83837)

## About The Pull Request
This pr gives a unique sprite to envyknife which is made by
sylvia-from-fulp-station
which looks like

![image](https://github.com/tgstation/tgstation/assets/24854897/1e8ef872-33c1-486a-9c3d-eb87169931ce)

and how it looks bloodied(i personally i think the overlays look pretty
cool this way)

![image](https://github.com/tgstation/tgstation/assets/24854897/a792f07c-7d52-4308-b492-c4a24e3f3ef9)



## Why It's Good For The Game
Currently envyknife looks like a cult dagger which can be mistaken from
an auctall antag this gives the envy knife a little more personality as
a lavaland ruin item

## Changelog

:cl: sylvia-from-fulp-station
image: Adds a unique sprite for envyknife
/:cl:

code/modules/mapfluff/ruins/objects_and_mobs/sin_ruins.dm

@@ -26,8 +26,8 @@
 /obj/item/knife/envy //Envy's knife: Found in the Envy ruin. Attackers take on the appearance of whoever they strike.
  name = "envy's knife"
  desc = "Their success will be yours."
- icon = 'icons/obj/weapons/khopesh.dmi'
- icon_state = "render"
+ icon = 'icons/obj/weapons/stabby.dmi'
+ icon_state = "envyknife"
  inhand_icon_state = "knife"
  lefthand_file = 'icons/mob/inhands/equipment/kitchen_lefthand.dmi'
  righthand_file = 'icons/mob/inhands/equipment/kitchen_righthand.dmi'