Refactor matrix; add push jobs to run on main only

.github/workflows/build.yml

@@ -0,0 +1,34 @@
+name: Build Docker images
+
+on:
+  pull_request:
+  push:
+    branches-ignore: 'main'
+
+jobs:
+  ubuntu:
+    strategy:
+      matrix:
+        arch:
+          - arm64
+          - x86_64
+        distro:
+          - focal
+          - jammy
+          - latest
+        include:
+          - arch: arm64
+            runner: oqs-arm64
+          - arch: x86_64
+            runner: ubuntu-latest
+    runs-on: ${{ matrix.runner }}
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Build image
+        uses: docker/build-push-action@v6
+        with:
+          push: false
+          build-args: ARCH=${{ matrix.arch }}
+          tags: openquantumsafe/ci-ubuntu-${{ matrix.distro }}:latest-${{ matrix.arch }}
+          context: ubuntu-${{ matrix.distro }}

.github/workflows/ci.yml → .github/workflows/push.yml

@@ -2,6 +2,7 @@ name: Build and push Docker images
 
 on:
   push:
+    branches: 'main'
 
 jobs:
   ubuntu-arm64:
@@ -15,10 +16,15 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
-      - name: Build arm64 tag
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ vars.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      - name: Build and push arm64 tag
         uses: docker/build-push-action@v6
         with:
-          # push: true
+          push: true
           build-args: ARCH=arm64
           tags: openquantumsafe/ci-ubuntu-${{ matrix.distro }}:latest-arm64
           context: ubuntu-${{ matrix.distro }}
@@ -35,10 +41,22 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
+      - name: Login to Docker Hub
+        if: github.ref_name == 'main'
+        uses: docker/login-action@v3
+        with:
+          username: ${{ vars.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
       - name: Build and push x86_64 tag
         uses: docker/build-push-action@v6
         with:
-          # push: true
+          push: true
           build-args: ARCH=x86_64
           tags: openquantumsafe/ci-ubuntu-${{ matrix.distro }}:latest-x86_64
           context: ubuntu-${{ matrix.distro }}
+      - name: Create multiarch image
+        run: |
+          docker manifest create openquantumsafe/ci-ubuntu-${{ matrix.distro }}:latest \
+            --amend openquantumsafe/ci-ubuntu-${{ matrix.distro }}:latest-x86_64 \
+            --amend openquantumsafe/ci-ubuntu-${{ matrix.distro }}:latest-arm64 \
+            && docker manifest push openquantumsafe/ci-ubuntu-${{ matrix.distro }}:latest