example docker compose file and test

.forgejo/workflows/example-docker-compose.yml

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+# SPDX-License-Identifier: MIT
+on: [push]
+
+jobs:
+  example-docker-compose:
+    runs-on: self-hosted
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install docker
+        run: |
+          apt-get update -qq
+          export DEBIAN_FRONTEND=noninteractive
+          apt-get install -qq -y ca-certificates curl gnupg
+          install -m 0755 -d /etc/apt/keyrings
+          curl -fsSL https://download.docker.com/linux/debian/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
+          echo "deb [arch="$(dpkg --print-architecture)" signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/debian "$(. /etc/os-release && echo "$VERSION_CODENAME")" stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
+          apt-get update -qq
+          apt-get install -qq -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin=2.20.2-1~debian.11~bullseye
+          docker version
+          #
+          # docker compose is prone to non backward compatible changes, pin it
+          #
+          apt-get install -qq -y docker-compose-plugin=2.20.2-1~debian.11~bullseye
+          docker compose version
+
+      - name: run the example
+        run: |
+          set -x
+          cd examples/docker-compose
+          cli="docker compose -f compose-forgejo-and-runner.yml -f compose-demo-workflow.yml"
+          #
+          # Launch
+          #
+          $cli up -d
+          #
+          # Wait for the demo workflow to complete
+          #
+          $cli ps --help
+          success='DEMO WORKFLOW SUCCESS'
+          for delay in $(seq 60) ; do
+            $cli logs -n 10 demo-workflow > /tmp/out
+            grep --quiet "$success" /tmp/out && break
+            $cli ps --all
+            cat /tmp/out
+            sleep 10
+          done
+          if ! grep --quiet "$success" /tmp/out ; then
+            echo ==========================================
+            $cli logs
+            exit 1
+          fi