Merge branch 'fix-concretizer' into 'master'

Switch to new concretizer config

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!186

spack.yaml

@@ -68,4 +68,5 @@ spack:
     #- sda
     # demo for codejam12
     #- funniest1022
-  concretization: together
+  concretizer:
+    unify: true