ADD: opal to stable stage RHEL

env/rhel7/x86_64/admin/stable/spack.yaml

@@ -1,14 +1,20 @@
----
 spack:
   concretizer:
     unify: false
   config:
     install_tree:
       root: $spack/opt/spack/stable
+  definitions:
+    - gcc_12.3.0_openmpi:
+      - opal@master/l4dkgyf
   include:
   - $spack/spack-psi/env/rhel7/$target_family/sysconfigs/packages.yaml
   - $spack/spack-psi/env/rhel7/$target_family/sysconfigs/compilers.yaml
   mirrors:
     local_psi: file:///afs/psi.ch/software/spack/testing
-  specs: []
+  specs:
+  - matrix:
+    - [$gcc_12.3.0_openmpi]
+    - [^openmpi%gcc]
+    - ['%gcc@12.3.0']
   view: false