$ git clone -n https://src.fedoraproject.org/rpms/rubygem-pkg-config.git /var/lib/mock/f42-build-side-1-3536528-46558/root/chroot_tmpdir/scmroot/rubygem-pkg-config
Cloning into '/var/lib/mock/f42-build-side-1-3536528-46558/root/chroot_tmpdir/scmroot/rubygem-pkg-config'...
$ git fetch origin 20cd924a0556467a2259c10479d7b5858fa3fad1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-pkg-config
 * [new ref]         20cd924a0556467a2259c10479d7b5858fa3fad1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 20cd924 1.6.2