handle no default attestations env var

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

Author: crazy-max

.github/workflows/ci.yml

@@ -1542,3 +1542,26 @@ jobs:
             echo "::error::Should have failed"
             exit 1
           fi
+
+  no-default-attestations:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v4
+        with:
+          path: action
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+        with:
+          version: ${{ inputs.buildx-version || env.BUILDX_VERSION }}
+          driver-opts: |
+            image=${{ inputs.buildkit-image || env.BUILDKIT_IMAGE }}
+      -
+        name: Build
+        uses: ./action
+        with:
+          file: ./test/Dockerfile
+        env:
+          BUILDX_NO_DEFAULT_ATTESTATIONS: 1