Document temp dir retention in how-to guide

[faph]

I discovered by accident Pytest's feature to retain temporary directories by default after tests complete. I feel the how-to guide "How to use temporary directories and files in tests" (https://docs.pytest.org/en/7.1.x/how-to/tmp_path.html) could do with documenting this feature as this may be the first and only page a developer reads before using the tmp_path fixture.

Currently, the documentation simply refers to "a temporary directory unique to the test (...)". As an engineer, I read that as something that goes away automatically as soon as the fixture is being tore down.

This may be an issue when using large temporary files, for example, in automated pipelines.

I don't mind what wording is used, but a reference to the API reference docs (e.g. https://docs.pytest.org/en/7.3.x/reference/reference.html#confval-tmp_path_retention_policy) might be extremely useful.