$ git clone -n https://src.fedoraproject.org/rpms/R-promises.git /var/lib/mock/f38-build-724176-99404/root/chroot_tmpdir/scmroot/R-promises
Cloning into '/var/lib/mock/f38-build-724176-99404/root/chroot_tmpdir/scmroot/R-promises'...
$ git fetch origin e1c09b1ca445720e8021d489a1ef13e75848229d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-promises
 * [new ref]         e1c09b1ca445720e8021d489a1ef13e75848229d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e1c09b1 R-maint-sig mass rebuild