Limit parallelism of buildx builds

.github/buildkit.toml

@@ -0,0 +1,2 @@
+[worker.oci]
+  max-parallelism = 4

.github/workflows/build.yml

@@ -75,6 +75,8 @@ jobs:
         uses: actions/checkout@v2
       - name: Install buildx
         uses: docker/setup-buildx-action@v1
+        with:
+          config: .github/buildkit.toml
       - name: Generate Dockerfile
         run: ./generate.sh ${{ matrix.target }} ${{ matrix.variant }}
       - name: Login to Docker

.github/workflows/pr.yml

@@ -22,6 +22,10 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v2
+      - name: Install buildx
+        uses: docker/setup-buildx-action@v1
+        with:
+          config: .github/buildkit.toml
       - name: Build Image
         run: ./makeimage.sh ${{ matrix.target }} ${{ matrix.variant }}
       - name: Build ffmpeg