ruff

2923c556 - [ty] Add test coverage for `PythonEnvironment::System` variants (#17996)

[ty] Add test coverage for `PythonEnvironment::System` variants (#17996) Adds test coverage for https://github.com/astral-sh/ruff/pull/17991, which includes some minor refactoring of the virtual environment test infrastructure. I tried to minimize stylistic changes, but there are still a few because I was a little confused by the setup. I could see this evolving more in the future, as I don't think the existing model can capture all the test coverage I'm looking for.