Modify Hello World in Grain (#4176)

Use official Grain docker image

Author: rzuckerm

archive/g/grain/hello-world.gr

@@ -1 +1,3 @@
-print('Hello, World!')
+module Main
+
+print("Hello, World!")

archive/g/grain/testinfo.yml

@@ -3,6 +3,6 @@ folder:
   naming: "hyphen"
 
 container:
-  image: "nickbreaton/grain"
-  tag: "latest"
+  image: "ghcr.io/grain-lang/grain"
+  tag: "0.6.6-slim"
   cmd: "grain {{ source.name }}{{ source.extension }}"