Skip package management if running in github-hosted container

GitHub allows running actions in containers [1] on the runners, and when
using a non apt-based Linux distribution, setup-ocaml doesn't work
correctly. This commit skips package management on docker containers,
similar to the behavior on self-hosted runners.

[1]: https://docs.github.com/en/actions/writing-workflows/choosing-where-your-workflow-runs/running-jobs-in-a-container

Author: punchagan

.github/workflows/workflow.yml

@@ -77,3 +77,31 @@ jobs:
           allow-prerelease-opam: ${{ matrix.allow-prerelease-opam }}
 
       - run: opam install ssl
+
+  test-container:
+    name: Test on a container in a GitHub runner
+
+    needs: hygiene
+
+    runs-on: ubuntu-24.04
+
+    container:
+      image: archlinux:latest
+
+    steps:
+      - name: Checkout tree
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+
+      - name: Install pre-requisites
+        run: |
+          pacman -Sy --noconfirm make gcc patch tar ca-certificates git \
+              rsync curl sudo bash nano coreutils xz ncurses diffutils \
+              unzip
+
+      - name: Set-up OCaml ${{ matrix.ocaml-compiler }}
+        uses: ./
+        with:
+          ocaml-compiler: "5.3"
+          opam-disable-sandboxing: true
+
+      - run: opam install ssl