Fix tag variable for build job

Author: juffalow

.github/workflows/main.yml

@@ -79,6 +79,9 @@ jobs:
     - uses: actions/checkout@v2
       with:
         fetch-depth: 1
+    - name: Set variables
+      id: vars
+      run: echo ::set-output name=tag::${GITHUB_REF#refs/*/}
     - name: Configure AWS credentials
       uses: aws-actions/configure-aws-credentials@v1
       with:
@@ -92,7 +95,7 @@ jobs:
       env:
         REGISTRY: ${{ steps.login-ecr.outputs.registry }}
         REPOSITORY: express-graphql-example
-        TAG: ${GITHUB_REF#"refs/tags/"}
+        TAG: ${{ steps.vars.outputs.tag }}
       run: |
         docker build -t $REGISTRY/$REPOSITORY:$TAG .
         docker push $REGISTRY/$REPOSITORY:$TAG