Fixes plumbing ducts having weird shadows (#96102)

## About The Pull Request

UPDATE_ICON is needed rather than UPDATE_ICON_STATE to update the
emissive blocker
Closes #96076

## Changelog
🆑
fix: Fixed plumbing ducts having weird shadows
/🆑

code/datums/components/plumbing/_plumbing.dm

@@ -100,7 +100,7 @@
 			if(istype(duct))
 				if(duct.neighbours && (duct.duct_layer & ducting_layer))
 					duct.neighbours[parent] = opposite_dir
-					duct.update_appearance(UPDATE_ICON_STATE)
+					duct.update_appearance(UPDATE_ICON)
 					duct.net.add_plumber(src, direction)
 				continue
 
@@ -123,7 +123,7 @@
 		for(var/obj/machinery/duct/pipe as anything in net.ducts)
 			if(pipe.neighbours[parent])
 				pipe.neighbours -= parent
-				pipe.update_appearance(UPDATE_ICON_STATE)
+				pipe.update_appearance(UPDATE_ICON)
 
 		//remove ourself from this network and delete it if emtpy
 		if(net.remove_plumber(src))

code/modules/plumbing/ducts.dm

@@ -114,7 +114,7 @@
 				neighbours[other] = direction
 				//connecting duct to us
 				LAZYADDASSOC(other.neighbours, src, opposite_dir)
-				other.update_appearance(UPDATE_ICON_STATE)
+				other.update_appearance(UPDATE_ICON)
 
 				continue
 
@@ -138,7 +138,7 @@
 				//assign neighbour
 				neighbours[plumbing.parent] = direction
 
-	update_appearance(UPDATE_ICON_STATE)
+	update_appearance(UPDATE_ICON)
 
 ///we disconnect ourself from our neighbours. we also destroy our ductnet and tell our neighbours to make a new one
 /obj/machinery/duct/on_deconstruction()
@@ -168,7 +168,7 @@
 		var/obj/machinery/duct/pipe = neighbour
 		if(istype(pipe))
 			pipe.neighbours -= src
-			pipe.update_appearance(UPDATE_ICON_STATE)
+			pipe.update_appearance(UPDATE_ICON)
 
 		//find every node that can be reached from our neighbour making sure to not revisit it again in circles
 		if(visited[neighbour])