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

Author: Sam Harrison

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

@@ -15,12 +15,21 @@ jobs:
     name: Test
     runs-on: ubuntu-latest
     timeout-minutes: 20
+    env:
+      DOCKER_LOGIN: ${{ secrets.DOCKER_USERNAME && secrets.DOCKER_AUTH_TOKEN }}
     steps:
       - name: Checkout sendgrid-csharp
         uses: actions/checkout@v2
         with:
           fetch-depth: 0
 
+      - name: Login to Docker Hub
+        if: env.DOCKER_LOGIN
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_AUTH_TOKEN }}
+
       - name: Setup .NET Core SDK
         uses: actions/[email protected]
         with: