Avoid panic when `typename` is provided as a keyword argument (#6955)
## Summary
The `typename` argument to `NamedTuple` and `TypedDict` is a required
positional argument. We assumed as much, but panicked if it was provided
as a keyword argument or otherwise omitted. This PR handles the case
gracefully.
Closes https://github.com/astral-sh/ruff/issues/6953.