Update docker-build.yml

Author: iamacarpet

.github/workflows/docker-build.yml

@@ -10,6 +10,8 @@ jobs:
   build-and-push-image:
     runs-on: ubuntu-latest
     steps:
+    - name: Checkout
+      uses: actions/checkout@v2
     - name: Build container image
       uses: docker/build-push-action@v1
       with: