Install UFW on the GH Actions runner (i.e., the Docker host)

.github/workflows/build.yml

@@ -192,6 +192,14 @@ jobs:
         uses: step-security/harden-runner@v2
         with:
           egress-policy: audit
+      # This ensures that whatever code (libraries, kernel modules,
+      # etc.) required on the Docker host to support running UFW in a
+      # Docker container is installed.
+      - id: install-ufw-host
+        name: Install UFW on the host
+        run: |
+          sudo apt-get update
+          sudo apt-get install ufw
       - id: setup-env
         uses: cisagov/setup-env-github-action@develop
       - uses: actions/checkout@v4