CI: Add Arch Linux to the test matrix

Recently, there was a regression because a parameter has been introduced
which is only present for Red Hat and Debian systems. When adding other
Linux distributions to the test suite, errors like this might get caught
in the future.

.github/workflows/ci.yml

@@ -39,8 +39,10 @@ jobs:
     name: Molecule
     runs-on: ubuntu-latest
     strategy:
+      fail-fast: false
       matrix:
         distro:
+          - archlinux
           - rockylinux8
           - centos7
           - ubuntu2004
@@ -64,9 +66,24 @@ jobs:
       - name: Install test dependencies.
         run: pip3 install ansible molecule[docker] docker
 
+      - name: Provide MOLECULE_DISTRO to environment
+        run: echo "MOLECULE_DISTRO=${{ matrix.distro || 'centos7' }}" >> $GITHUB_ENV
+
       - name: Run Molecule tests.
+        if: matrix.distro != 'archlinux'
         run: molecule test
         env:
           PY_COLORS: '1'
           ANSIBLE_FORCE_COLOR: '1'
-          MOLECULE_DISTRO: ${{ matrix.distro }}
+          CI_IMAGE: geerlingguy/docker-${{ env.MOLECULE_DISTRO }}-ansible:latest
+
+      - name: Run Molecule tests on Arch Linux.
+        if: matrix.distro == 'archlinux'
+        run: molecule test
+        env:
+          PY_COLORS: '1'
+          ANSIBLE_FORCE_COLOR: '1'
+          # CI_IMAGE: mesaguy/ansible-molecule-archlinux:latest
+          # CI_IMAGE: carlodepieri/docker-archlinux-ansible:latest
+          # CI_IMAGE: ghcr.io/avnes/molecule-arch:latest
+          CI_IMAGE: archlinux:base-20210328.0.18194

molecule/default/molecule.yml

@@ -5,10 +5,13 @@ driver:
   name: docker
 platforms:
   - name: instance
-    image: "geerlingguy/docker-${MOLECULE_DISTRO:-centos7}-ansible:latest"
+    image: ${CI_IMAGE}
     command: ${MOLECULE_DOCKER_COMMAND:-""}
+    tmpfs:
+      - /run
+      - /tmp
     volumes:
-      - /sys/fs/cgroup:/sys/fs/cgroup:ro
+      - /sys/fs/cgroup:/sys/fs/cgroup:rw
     privileged: true
     pre_build_image: true
 provisioner: