docs: update workflow to refer to local repo

.github/workflows/gh-pages.yaml

@@ -7,14 +7,17 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
+        with:
+          path: collections/ansible_collections/sophos/sophos_firewall
       - uses: actions/setup-python@v3
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
           pip install -r docs/requirements.txt
           pip install ansible
-          ansible-galaxy collection install sophos.sophos_firewall
       - name: Sphinx build
+        env:
+          ANSIBLE_COLLECTIONS_PATH: "$GITHUB_WORKSPACE/collections"
         run: |
           bash docs/build.sh
       - name: Deploy