Add missing test files to CI matrix

The matrix in test.yml was missing entries for several test files and
docs, so those tests were never run in CI. Add them now that
test_tests_collected_once actually verifies coverage.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: adamtheturtle

.github/workflows/test.yml

@@ -113,11 +113,15 @@ jobs:
           - tests/mock_vws/test_update_target.py::TestWidth
           - tests/mock_vws/test_update_target.py::TestInactiveProject
           - tests/mock_vws/test_requests_mock_usage.py
+          - tests/mock_vws/test_respx_mock_usage.py
           - tests/mock_vws/test_flask_app_usage.py
           - tests/mock_vws/test_vumark_generation_api.py
+          - tests/mock_vws/test_target_validators.py
           - tests/mock_vws/test_docker.py
+          - ci/test_custom_linters.py
           - README.rst
           - docs/source/basic-example.rst
+          - docs/source/httpx-example.rst
 
     steps:
       - uses: actions/checkout@v6