mypy: Fix all index

[Avasam]

No description provided.

[Avasam]

There's a decision to be taken here.

1. Don't support PathLike in this branch (current behaviour)
2. Don't support bytes | PathLike[bytes] in this branch

Suggested change

	# type-ignore: This makes absolutes os.Pathlike unsupported in this branch.
	# Either this or we don't support bytes-based paths, or we complexify this branch.
	return os.path.join(new_root, pathname[1:]) # type: ignore[index]
	# type-ignore: This makes absolutes os.Pathlike unsupported in this branch.
	# Either this or we don't support bytes-based paths, or we complexify this branch.
	return os.path.join(new_root, str(pathname)[1:])

3. Support both, requires extra checking.