ci: Initialize git submodules in GitHub Actions workflow

Fix test failure for test_cli_all_flag_lists_configs by ensuring
api/configs_repo submodule is initialized during checkout.

The test expects configs in api/configs_repo/official/ but the
submodule was not being initialized, causing the directory to be
empty and the test to fail.

Related:
- Commit 1cbb8fe: Added api/configs_repo as git submodule
- Commit f5f37f6: Updated render.yaml for Render deployment

This completes the submodule integration for both:
- Production (Render API deployment)
- CI/CD (GitHub Actions tests)

Fixes: FAILED tests/test_estimate_pages.py::TestEstimatePagesCLI::test_cli_all_flag_lists_configs

.github/workflows/tests.yml

@@ -21,6 +21,8 @@ jobs:
 
     steps:
     - uses: actions/checkout@v3
+      with:
+        submodules: recursive  # Initialize api/configs_repo submodule
 
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v4