tests/cp/preserve-gid: `cp -p` fails to preserve group

[drinkcat]

Looks like I didn't fix everything in #8380...

Steps (assumes users/groups 1002/1003/1004 don't exist):

mkdir t
chmod a+rwx t
touch t/b1 && sudo chown 1002:1004 t/b1
rm -f t/b
sudo chroot --skip-chdir --user=+1002:+1003 --groups=+1003,+1004 / cp -p t/b1 t/b
ls -l t
total 0
-rw-r--r-- 1 1002 1004 0 Aug  8 18:33 b
-rw-r--r-- 1 1002 1004 0 Aug  8 18:33 b1
rm -f t/b
sudo chroot --skip-chdir --user=+1002:+1003 --groups=+1003,+1004 / target/debug/cp -p t/b1 t/b
ls -l t
total 0
-rw-r--r-- 1 1002 1003 0 Aug  8 18:37 b
-rw-r--r-- 1 1002 1004 0 Aug  8 18:33 b1

[drinkcat]

I think the problem is that canonicalize fails if the user doesn't have read access to the entirety of the path (which is what that chroot thing causes).

This was introduced in #6446, I can easily workaround the issue but I want to check all uses of canonicalize...

This is also broken:

mkdir t/x1 && sudo chown 1002:1004 t/x1 && sudo chmod 0707 t/x1
touch t/x1/b1 && sudo chown 1002:1004 t/x1/b1
sudo rm -rf t/x; mkdir -m 0777 t/x; sudo chroot --skip-chdir --user=+1002:+1003 --groups=+1003,+1004 / target/debug/cp --parents -p t/x1 t/x; ls -lR t