Try v0.23.1 Spack buildcache.

Author: nkoukpaizan

.github/workflows/spack_default_build.yaml

@@ -7,7 +7,7 @@ env:
   # Our repo name contains upper case characters, so we can't use ${{ github.repository }}
   IMAGE_NAME: gridkit
   USERNAME: gridkit-bot
-  BASE_VERSION: ubuntu-24.04-fortran-v0.2.7
+  BASE_VERSION: ubuntu-24.04-fortran-v0.2.8
 
 # Until we remove the need to clone submodules to build, this should on be in PRs
 on: [pull_request]
@@ -97,8 +97,7 @@ jobs:
       matrix:
         # Minimal Build(s) - GHCR mirror speeds these up a lot!
         spack_spec:
-          - llvm@16
-          #- gridkit@develop +enzyme
+          - gridkit@develop +enzyme
 
     name: Build gridkit with Spack
     steps:
@@ -126,7 +125,12 @@ jobs:
                 padded_length: 128
             mirrors:
               local-buildcache: oci://${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
-              spack: https://binaries.spack.io/develop
+              spack: https://binaries.spack.io/v0.23.1
+            packages:
+              llvm:
+                externals:
+                - spec: llvm@16
+                  prefix: /usr/lib/llvm-16
           EOF
 
       - name: Configure GHCR mirror