GHA: test apptainer workflow

.github/workflows/apptainer.yaml

@@ -0,0 +1,49 @@
+name: apptainer
+
+on:
+  push:
+    branches:
+      - apptainer
+
+env:
+  VERSION: '1.4.1.9006' # versioned by bump2version
+jobs:
+  docker2apptainer:
+    name: Docker2apptainer
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        shell: bash -l {0}
+    steps:
+      - name: Code checkout
+        uses: actions/checkout@v4
+        with:
+          ref: v${{ env.VERSION }}
+      - name: 🏰 QEMU setup
+        uses: docker/setup-qemu-action@v3
+      - name: 🏯 Buildx setup
+        uses: docker/setup-buildx-action@v3
+      - name: DockerHub login
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      - name: 🐳 Docker img build and push to DockerHub
+        uses: docker/build-push-action@v5
+        with:
+          context: . # yes, dot
+          push: true
+          load: true
+          platforms: linux/amd64
+          tags: |
+            sigven/pcgr:${{ env.VERSION }}
+
+      - name: Apptainer setup
+        uses: eWaterCycle/setup-apptainer@v2
+
+      - name: Apptainer build
+        run: |
+          docker image ls -a
+          docker save sigven/pcgr:${VERSION} -o pcgr_${VERSION}.tar
+          apptainer build pcgr_${VERSION}.sif docker-archive://pcgr_${VERSION}.tar
+          apptainer push pcgr_${VERSION}.sif oras://ghcr.io/${GITHUB_REPOSITORY}:${VERSION}