ADD: env testing must be clean before new installation

env/sles15/aarch64/admin/testing/spack.yaml

@@ -1,6 +1,12 @@
 spack:
   concretizer:
-    unify: false
+    unify: when_possible
+    targets:
+      granularity: microarchitectures
+    reuse:
+      from:
+      - type: local
+      - type: external
   config:
     install_tree:
       root: $spack/opt/spack/testing
@@ -8,7 +14,6 @@ spack:
       padded_length: 256
   include:
   - $spack/../spack-psi/env/$os/$target_family/sysconfigs/packages.yaml
-  - $spack/../spack-psi/env/$os/$target_family/sysconfigs/compilers.yaml
   mirrors:
     local_psi: file:///afs/psi.ch/software/spack/testing
   modules: