Explicitly use buildx for local script

.github/workflows/pr.yml

@@ -26,6 +26,7 @@ jobs:
         uses: docker/setup-buildx-action@v1
         with:
           config: .github/buildkit.toml
+          driver: docker
       - name: Build Image
         run: ./makeimage.sh ${{ matrix.target }} ${{ matrix.variant }}
       - name: Build ffmpeg