Create an issue @ Docker repository on tag

.github/workflows/release.yml

@@ -56,3 +56,20 @@ jobs:
           asset_path: ./composer.phar
           asset_name: composer.phar
           asset_content_type: application/octet-stream
+
+      # This step requires a secret token with `pull` access to composer/docker. The default
+      # secrets.GITHUB_TOKEN is scoped to this repository only which is not sufficient.
+      - name: "Open issue @ Docker repository"
+        uses: actions/github-script@v2
+        with:
+          github-token: ${{ secrets.PUBLIC_REPO_ACCESS_TOKEN }}
+          script: |
+            // github.ref value looks like 'refs/tags/TAG', cleanup
+            const tag = "${{ github.ref }}".replace(/refs\/tags\//, '');
+            // create new issue on Docker repository
+            github.issues.create({
+              owner: "${{ github.repository_owner }}",
+              repo: "docker",
+              title: `New Composer tag: ${ tag }`,
+              body: `https://github.com/${{ github.repository }}/releases/tag/${ tag }`,
+            });