output concretized specs before install

Author: plexoos

.github/workflows/build-push-spack-buildcache.yaml

@@ -70,6 +70,10 @@ jobs:
               spack mirror add --autopush --unsigned --oci-username-variable REGISTRY_USER --oci-password-variable REGISTRY_TOKEN simphony-spack-buildcache "${SPACK_BUILDCACHE_MIRROR}"
               spack external find --not-buildable --path /usr/local/cuda cuda
 
+              echo "::group::Concretized simphony spec before install"
+              spack spec --fresh -Il simphony ^geant4@${GEANT4_VERSION} ^optix-dev@${OPTIX_VERSION}
+              echo "::endgroup::"
+
               # Solve fresh against current package metadata, but still install exact matches
               # from the mirror. Autopush dependencies as soon as source builds complete, so
               # partial progress survives a failed long-running buildcache refresh.