`nox --session lint` does not consider test directory

[Preocts]

Reproduction steps:

1. Reorder imports in ./tests/sample_test.py
2. Remove __from__ future import annotations from ./tests/sample_test.py
3. Run nox --session lint
4. Note that all files in ./tests have been missed for linting

Desired outcome:

Capture all files in the ./src and ./tests directories.