Use latest stable cardano-node in demo

The docker variant was broken as the conway-genesis.json was not
parseable using the old 8.7.3 node and we seemingly have forgotten to
update this container when we started to test against cardano-node 8.9

demo/docker-compose.yaml

@@ -2,7 +2,7 @@ version: "3.9"
 
 services:
   cardano-node:
-    image: ghcr.io/input-output-hk/cardano-node:8.7.3
+    image: ghcr.io/intersectmbo/cardano-node:8.9.1
     volumes:
       - ./devnet:/devnet
     environment: