$ git clone -n https://src.fedoraproject.org/rpms/perl-Math-BigInt.git /var/lib/mock/f42-build-side-1-3499888-45966/root/chroot_tmpdir/scmroot/perl-Math-BigInt
Cloning into '/var/lib/mock/f42-build-side-1-3499888-45966/root/chroot_tmpdir/scmroot/perl-Math-BigInt'...
$ git fetch origin e407fa079e5e820899e90091691aa02b17329483:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/perl-Math-BigInt
 * [new ref]         e407fa079e5e820899e90091691aa02b17329483 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e407fa0 2.004001 bump (rhbz#2349247)