$ git clone -n https://src.fedoraproject.org/rpms/R-git2r /var/lib/mock/f39-build-1582042-38102/root/chroot_tmpdir/scmroot/R-git2r
Cloning into '/var/lib/mock/f39-build-1582042-38102/root/chroot_tmpdir/scmroot/R-git2r'...
$ git fetch origin d0b696cfba32f42bc04acfb1775259d5a350113c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-git2r
 * [new ref]         d0b696cfba32f42bc04acfb1775259d5a350113c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at d0b696c Rebuild for libgit2 1.7.x