set env var for sops to use for auth

.github/workflows/deploy-to-staging.yaml

@@ -78,6 +78,7 @@ jobs:
       - name: Deploy hubs to staging
         if: ${{ env.DEPLOY }}
         run: |
+          GOOGLE_APPLICATION_CREDENTIALS=${{ secrets.GKE_KEY }}
           for hub in $(echo -e "${{ env.DEPLOY_HUBS }}"); do
             echo "Deploying $hub to staging"
             hubploy --verbose deploy $hub hub staging