If base directories (e.g. $HOME/.config/fish) need to be created,
create them with mode 0700 (i.e. restricted to the owner).
This both keeps the behavior of old fish versions (e.g. 3.7.1) and is
compliant with the XDG Base Directory Specification.
See: https://specifications.freedesktop.org/basedir-spec/0.8/#referencing
