Build docker images with spack inside

This prevents that the executing runner needs to be prepared to access GitHub

.gitlab-ci.yml

@@ -1,14 +1,12 @@
 ---
 
 before_script:
-  - git clone -b v$SPACK_VERSION https://github.com/spack/spack.git
-  - . ./spack/share/spack/setup_env.sh
+  - pwd
+  - . /spack/share/spack/setup-env.sh
   - spack repo add .
 
-image: registry.dune-project.org/docker/ci/debian:10
-
 spectest:v0.14.2:
-  variables:
-    - SPACK_VERSION : "0.14.2"
-  script:
-    - spack spec dune
+  image: registry.dune-project.org/spack/dune-spack:v0.14.2
+  script: spack spec dune
+  tags:
+    - cores:1