parallelize CI build even further

passenger-full takes 3.75 hours without this

.github/workflows/main.yml

@@ -13,10 +13,13 @@ defaults:
 jobs:
   build:
     name: "build-${{ matrix.img }}"
-    runs-on: ubuntu-latest
+    runs-on: [ ubuntu, linux, ${{ matrix.arch }} ]
     strategy:
       fail-fast: true
       matrix:
+        arch:
+         - arm64
+         - amd64
         img:
          - full
          - customizable
@@ -44,6 +47,9 @@ jobs:
         run: 'docker run --privileged --rm tonistiigi/binfmt --install all'
       - name: "Run make build_${{ matrix.img }}"
         run: "make build_${{ matrix.img }}"
+        env:
+          BUILD_AMD64: ${{ fromJSON('[1, 0]')[matrix.arch == 'amd64'] }}
+          BUILD_ARM64: ${{ fromJSON('[1, 0]')[matrix.arch == 'arm64'] }}
       - name: Log in to the Container registry
         if: ${{ github.event.pull_request.merged || github.actor == 'CamJN' }}
         uses: docker/login-action@v3
@@ -55,3 +61,6 @@ jobs:
       - name: Push to github container registry
         if: ${{ success() && steps.login.conclusion != 'skipped' }}
         run: "make release_${{ matrix.img }}"
+        env:
+          BUILD_AMD64: ${{ fromJSON('[1, 0]')[matrix.arch == 'amd64'] }}
+          BUILD_ARM64: ${{ fromJSON('[1, 0]')[matrix.arch == 'arm64'] }}