scripts/t: Do not try to sign test packages

If GnuPG is available in the build environment, dpkg-buildpackage will
use it to sign the .dsc and .changes files which fails because there is
no secret key for "Dpkg Developers <debian-dpkg@lists.debian.org>".

Signed-off-by: Guillem Jover <guillem@debian.org>

scripts/t/dpkg_buildpackage.t

@@ -181,6 +181,7 @@ sub test_build
 
     chdir $dirname;
     spawn(exec => [ "$srcdir/dpkg-buildpackage.pl", '--host-arch=amd64',
+                    '--unsigned-source', '--unsigned-changes',
                     "--build=$typename", '--check-command=' ],
           error_to_string => \$stderr,
           wait_child => 1, nocheck => 1);