Remove errant $ when defining groupId variable

Author: SvenAelterman

articles/container-instances/container-instances-github-action.md

@@ -51,7 +51,7 @@ In the GitHub workflow, you need to supply Azure credentials to authenticate to
 First, get the resource ID of your resource group. Substitute the name of your group in the following [az group show][az-group-show] command:
 
 ```azurecli
-$groupId=$(az group show \
+groupId=$(az group show \
   --name <resource-group-name> \
   --query id --output tsv)
 ```