$ git clone -n https://src.fedoraproject.org/rpms/mimalloc.git /var/lib/mock/f42-build-side-1-3502902-45979/root/chroot_tmpdir/scmroot/mimalloc
Cloning into '/var/lib/mock/f42-build-side-1-3502902-45979/root/chroot_tmpdir/scmroot/mimalloc'...
$ git fetch origin 4c89f49eb84bd716a698852791e2ea4307edf2c5:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mimalloc
 * [new ref]         4c89f49eb84bd716a698852791e2ea4307edf2c5 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4c89f49 Update to 2.2.3.