Add unit test for lock-file cleanup in pytest_configure

[gaurav]

Background

tests/conftest.py pytest_configure deletes both the Google Sheet CSV cache files and their .lock siblings at the start of each run. The lock-path bug (.csv.lock vs .lock) was fixed in PR #67, but there is no regression test covering this cleanup path.

What's missing

A unit/integration test that:

1. Creates a fake babel_validation_gsheet_<hash>.csv and its companion babel_validation_gsheet_<hash>.lock in tempfile.gettempdir().
2. Invokes the pytest_configure cleanup logic.
3. Asserts that both files are removed and that no .csv.lock stale file remains.

Without this test, a future refactor could silently reintroduce the same bug.

Notes

• Identified during the Opus code review of PR Add GitHub issue tests #67.
• The cleanup logic lives in tests/conftest.py::pytest_configure (lines 35–50).