This updates gnurl to version 7.70.0.

Something to consider (for gnurl and curl):
While all tests pass, gnurl and curl want the python module "impacket"
for some tests since bundled impacket got removed.

runtests.pl:
In the environment of guix, $USER is unset.

# get the name of the current user
my $USER = $ENV{USER};          # Linux
if (!$USER) {
    $USER = $ENV{USERNAME};     # Windows
    if (!$USER) {
        $USER = $ENV{LOGNAME};  # Some Unix (I think)
    }
}


leads to $USER being uninitialized at some point (around line 3600 or
something further below, grep for it). The tests loudly complain to the
log but it's not fatal.
Can I (as gnurl upstream) set a fallback value like "Anonymous" in the
next release, or what's your take on this?