Allow template_folder argument to be os.PathLike[str] as is allowed in Flask

[502E532E]

Quart currently supports only str | None for the template folder argument of the app, while Flask also supports os.PathLike[str]. https://github.com/pallets/quart/blob/b5593ca4c8c657564cdf2d35c9f0298fce63636b/src/quart/app.py#L287

flask/src/flask/app.py

template_folder: str | os.PathLike[str] | None = "templates",

As Quart seems to pass the argument directly to Flask.App, I do not think the further restriction is necessary.