Fix missing EOF for heredoc.

Author: Rutherford, Cameron

.github/workflows/spack_cpu_build.yaml

@@ -156,6 +156,7 @@ jobs:
             packages:
               all:
                 require: "%gcc"
+          EOF
 
       - name: Configure GHCR mirror
         run: spack -e . mirror set --oci-username ${{ env.USERNAME }} --oci-password "${{ secrets.GITHUB_TOKEN }}" local-buildcache