If we enter user namespace via regular unshare without help from SUID
newuidmap/newgidmap, all supplementary groups are mapped to -1. As the result
when Go test tries to chown to a supplementary group, it gets EINVAL:

https://github.com/golang/go/issues/42525

-> work it around with patch to skip this chown tests.

A more proper, longer-term fix would be to fix Linux kernel to allow writes to
/proc/self/gid_map to setup mapping not only to original gid, but to all
original supplementary groups as well here:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/user_namespace.c?id=v5.16-rc4-0-g0fcfb00b28c0#n1143

this fix, even if accepted by upstream, would be long to be waited for to
propagate to distribution kernels that we currently use. So we go with this
workaround for now.

--------

Another patch is to fix the following TestSCMCredentials failure:

    === RUN   TestSCMCredentials
        creds_test.go:81: WriteMsgUnix ...