fix: Set the Azure image version tag

The current latest image of Azure doesn't include apk. The last version before that (2.9.1) does. Maybe the current latest is broken or they're migrating away from Alpine. We'll see.

flavour/azure/Dockerfile.flavour

@@ -1,4 +1,4 @@
-FROM mcr.microsoft.com/azure-cli:latest
+FROM mcr.microsoft.com/azure-cli:2.9.1
 
 RUN apk add sudo bash curl && \
     echo "cloudcontrol ALL=(root)NOPASSWD:/sbin/apk *" > /etc/sudoers.d/cloudcontrol && \