FIX: Sync poetry.lock and drop Python 3.9 from CI matrix

[vcai4071]

Summary

• Regenerates poetry.lock so it matches the recent pyproject.toml dependency changes (pandas ^2, sphinx pin), fixing the CI lock-file validation failure.
• Removes Python 3.9 from the test matrix, since it is EOL and no longer preinstalled on GitHub-hosted runners.
• Bumps actions/setup-python from v4 to v5 for consistency with the other workflows.

Test plan

• CI Run Tests passes for Python 3.10, 3.11, and 3.12
• poetry check --lock succeeds locally