ci: simplify sbom

.github/workflows/docker-build.yml

@@ -48,6 +48,17 @@ jobs:
           release-count: 0 # preserve all versions in changelog
           skip-on-empty: false # otherwise we don't publish fixes
 
+      - name: Generate SBOM
+        uses: anchore/sbom-action@v0
+        id: sbom
+        if: ${{ steps.changelog.outputs.skipped == 'false' }}
+        with:
+          image: registry.dangerous.tech/dangeroustech/zerotierbridge:latest
+          registry-username: ${{ secrets.REGISTRY_USERNAME }}
+          registry-password: ${{ secrets.REGISTRY_PASSWORD }}
+          format: spdx-json
+          artifact-name: sbom.spdx.json
+
       - name: Create Release
         uses: softprops/action-gh-release@v1
         id: release
@@ -58,3 +69,5 @@ jobs:
           tag_name: ${{ steps.changelog.outputs.tag }}
           name: ${{ steps.changelog.outputs.tag }}
           body: ${{ steps.changelog.outputs.clean_changelog }}
+          files: |
+            sbom.spdx.json