[MIRROR] Shovel digging refactor (#12601)

Co-authored-by: Will <7099514+Willburd@users.noreply.github.com>
Co-authored-by: Cameron Lennox <killer65311@gmail.com>

code/modules/mining/mine_turfs.dm

@@ -382,6 +382,9 @@ GLOBAL_LIST_EMPTY(mining_overlay_cache)
 
 		if(istype(W, /obj/item/shovel))
 			var/obj/item/shovel/S = W
+			if(S.grave_mode)
+				shovel_dig_grave(user, S)
+				return
 			valid_tool = 1
 			digspeed = S.digspeed