ruff

1feb3cf4 - [red-knot] Use `Unknown | T_inferred` for undeclared public symbols (#15674)

[red-knot] Use `Unknown | T_inferred` for undeclared public symbols (#15674) ## Summary Use `Unknown | T_inferred` as the type for *undeclared* public symbols. ## Test Plan - Updated existing tests - New test for external `__slots__` modifications. - New tests for external modifications of public symbols.