ruff

fb58a9b6 - [red-knot] Rename `TestDbBuilder::typeshed` to `.custom_typeshed` (#15712)

[red-knot] Rename `TestDbBuilder::typeshed` to `.custom_typeshed` (#15712) ## Summary Correcting a small oversight by me (https://github.com/astral-sh/ruff/pull/15683#discussion_r1926830914).