generic: update setgid tests

generic: update setgid tests

Over mutiple kernel releases we have reworked setgid inheritance
significantly due to long-standing security issues, security issues that
were reintroduced after they were fixed, and the subtle and difficult
inheritance rules that plagued individual filesystems. We have lifted
setgid inheritance into the VFS proper in earlier patches. Starting with
kernel v6.2 we have made setgid inheritance consistent between the write
and setattr (ch{mod,own}) paths.

The gist of the requirement is that in order to inherit the setgid bit
the user needs to be in the group of the file or have CAP_FSETID in
their user namespace. Otherwise the setgid bit will be dropped
irregardless of the file's executability. Remove the obsolete tests as
they're not a security issue and will cause spurious warnings on older
distro kernels.

Note, that only with v6.2 setgid inheritance works correctly for
overlayfs in the write path. Before this the setgid bit was always
retained.

Link: https://lore.kernel.org/linux-ext4/CAOQ4uxhmCgyorYVtD6=n=khqwUc=MPbZs+y=sqt09XbGoNm_tA@mail.gmail.com
Link: https://lore.kernel.org/linux-fsdevel/20221212112053.99208-1-brauner@kernel.org
Link: https://lore.kernel.org/linux-fsdevel/20221122142010.zchf2jz2oymx55qi@wittgenstein
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Zorro Lang <zlang@redhat.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>