ci(spack): source setup-env.sh before spack load in smoke test

spack load uses shell functions (it modifies the calling shell's env)
which require sourcing share/spack/setup-env.sh. The install step works
without it because spack install is a plain executable. setup-spack
puts spack on PATH but each GH Actions step starts a fresh shell, so
shell-function support has to be reactivated per-step that needs it.

Author: sbryngelson

.github/workflows/spack.yml

@@ -26,6 +26,7 @@ jobs:
 
           - name: Smoke test
             run: |
+                source spack/share/spack/setup-env.sh
                 spack load mfc
                 prefix="$(spack location -i mfc)"
                 echo "MFC prefix: $prefix"