get tag from ref (to tag Docker image)

Author: kyoh86

.github/workflows/release.yml

@@ -23,6 +23,10 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GORELEASER_GITHUB_TOKEN }}
 
+      - name: Get the tag
+        id: get_tag
+        run: echo ::set-output name=TAG::${GITHUB_REF/refs\/tags\//}
+
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v1
       - name: Login to GitHub Container Registry
@@ -38,4 +42,4 @@ jobs:
           push: true
           tags: |
             ghcr.io/${{ github.repository_owner }}/git-vertag:latest
-            ghcr.io/${{ github.repository_owner }}/git-vertag:${{ github.event.tag_name }}
+            ghcr.io/${{ github.repository_owner }}/git-vertag:${{ steps.get_tag.outputs.TAG }}