$ git clone -n https://src.fedoraproject.org/rpms/R-promises.git /var/lib/mock/f42-build-side-1-3498658-45963/root/chroot_tmpdir/scmroot/R-promises
Cloning into '/var/lib/mock/f42-build-side-1-3498658-45963/root/chroot_tmpdir/scmroot/R-promises'...
$ git fetch origin dec10b56887fcb6a6dd061df987c31d0f7148dfa:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-promises
 * [new ref]         dec10b56887fcb6a6dd061df987c31d0f7148dfa -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at dec10b5 R-maint-sig mass rebuild