Use secret availability to determine whether to build/checkout hardened

Author: Metadorius

.github/workflows/nightly-build.yml

@@ -20,7 +20,7 @@ jobs:
         # this dimension is only needed to check whether we're in CnCNet repo
         # and exclude hardened build because we may have no access to it
         has-private-access:
-          - ${{ github.repository_owner == 'CnCNet' }}
+          - ${{ secrets.CNCNET_CI_SSH_PRIVATEKEY != '' }}
         exclude:
           - is-hardened: -Hardened
             has-private-access: false