Try system python in GH actions.

Author: nkoukpaizan

.github/workflows/spack_cpu_build.yaml

@@ -151,7 +151,7 @@ jobs:
         run: spack -e . buildcache keys --install --trust
 
       - name: Find external packages
-        run: spack -e . external find --all --exclude python
+        run: spack -e . external find --all
 
       - name: Spack develop exago
         run: spack -e . develop --path=$(pwd) exago@develop