$ git clone -n https://src.fedoraproject.org/rpms/rubygem-mysql2.git /var/lib/mock/f40-build-733974-105626/root/chroot_tmpdir/scmroot/rubygem-mysql2
Cloning into '/var/lib/mock/f40-build-733974-105626/root/chroot_tmpdir/scmroot/rubygem-mysql2'...
$ git fetch origin b357d260445484a7f8ccbb2ed55fc71b2841e74b:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-mysql2
 * [new ref]         b357d260445484a7f8ccbb2ed55fc71b2841e74b -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b357d26 Upgrade to rubygem-mysql2 0.5.5.