fix: only do a Docker Login if the secrets are available

Author: Sam Harrison

.github/workflows/test-and-deploy.yml

@@ -20,11 +20,13 @@ jobs:
         node: [ 6, 7, 8, 10, lts ]
     env:
       version: ${{ matrix.node }}
+      DOCKER_LOGIN: ${{ secrets.DOCKER_USERNAME && secrets.DOCKER_AUTH_TOKEN }}
     steps:
       - name: Checkout sendgrid-nodejs
         uses: actions/checkout@v2
 
       - name: Login to Docker Hub
+        if: env.DOCKER_LOGIN
         uses: docker/login-action@v1
         with:
           username: ${{ secrets.DOCKER_USERNAME }}