ci: add CI on s390x (#3463)

* ci: lay out foundation for s390x tests

* ci: uncomment the s390x test script & replace placeholders with real values

* ci: amend the s390x test job name to be more consistent with others

.github/workflows/ci.yml

@@ -120,6 +120,32 @@ jobs:
     #     echo "step_test ${{ steps.step_test.outputs.status }}\n"
     #     exit 1
 
+  s390x-test:
+    name: test (s390x on IBM Z)
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code into the Go module directory
+        uses: actions/checkout@v2
+      - name: Run Tests
+        run: |
+          mkdir -p ~/.ssh && echo -e "${SSH_KEY//_/\\n}" > ~/.ssh/id_ecdsa && chmod og-rwx ~/.ssh/id_ecdsa
+
+          # short sha is enough?
+          short_sha=$(git rev-parse --short HEAD)
+
+          # The environment is fresh, so there's no point in keeping accepting and adding the key.
+          rsync -arz -e "ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null" --progress --delete --exclude '.git' . caddy-ci@ci-s390x.caddyserver.com:/var/tmp/"$short_sha"
+          ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -t caddy-ci@ci-s390x.caddyserver.com "cd /var/tmp/$short_sha; CGO_ENABLED=0 /usr/local/go/bin/go test -v ./..."
+          test_result=$?
+
+          # There's no need leaving the files around
+          ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null caddy-ci@ci-s390x.caddyserver.com "rm -rf /var/tmp/'$short_sha'"
+
+          echo "Test exit code: $test_result"
+          exit $test_result
+        env:
+          SSH_KEY: ${{ secrets.S390X_SSH_KEY }}
+
   # From https://github.com/reviewdog/action-golangci-lint
   golangci-lint:
     name: runner / golangci-lint