idmapped-mounts: add missing ownership comparisons to setgid tests

idmapped-mounts: add missing ownership comparisons to setgid tests

In some setgid tests we missed to check ownership right after file or
directory creation in order to verify whether gid ownership inheritance
from the parent directory to the newly created file or directory works
correctly. Add the missing ones.

Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Eryu Guan <guaneryu@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: fstests@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>