Update docker/build-push-action action to v6.18.0

Author: renovate[bot]

.github/workflows/build-pypy.yml

@@ -45,7 +45,7 @@ jobs:
         uses: docker/setup-buildx-action@v3
 
       - name: Build Docker image
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@263435318d21b8e681c14492fe198d362a7d2c83 # v6.18.0
         with:
           context: "builder/"
           tags: ${{ env.BUILDER_IMAGE_TAG }}:${{ env.ALPINE_VERSION }}-${{ github.sha }}