chore: spack-0.20.0

containers/debian/base.Dockerfile

-#syntax=docker/dockerfile:1.2
-ARG BASE_IMAGE="amd64/debian:testing-20220822-slim"
-ARG BUILD_IMAGE="debian_base"
+#syntax=docker/dockerfile:1.4
+ARG BASE_IMAGE="amd64/debian:stable-slim"
+ARG BUILD_IMAGE="debian_stable_base"
 
 # Minimal container based on Debian base systems for up-to-date packages. 
 FROM  ${BASE_IMAGE}