$ git clone -n https://src.fedoraproject.org/rpms/R-brew.git /var/lib/mock/f39-build-1495948-34546/root/chroot_tmpdir/scmroot/R-brew
Cloning into '/var/lib/mock/f39-build-1495948-34546/root/chroot_tmpdir/scmroot/R-brew'...
$ git fetch origin aa3e7fc3b80dad0160f5fc6a09a51ac1fa298e28:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-brew
 * [new ref]         aa3e7fc3b80dad0160f5fc6a09a51ac1fa298e28 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at aa3e7fc Rebuilt for https://fedoraproject.org/wiki/Fedora_39_Mass_Rebuild