$ git clone -n https://src.fedoraproject.org/rpms/rust-headers.git /var/lib/mock/f39-build-1526406-36063/root/chroot_tmpdir/scmroot/rust-headers
Cloning into '/var/lib/mock/f39-build-1526406-36063/root/chroot_tmpdir/scmroot/rust-headers'...
$ git fetch origin 4929cb594163fb46b84964b1da0e0d6592427b38:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-headers
 * [new ref]         4929cb594163fb46b84964b1da0e0d6592427b38 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4929cb5 Update to version 0.3.9; Fixes RHBZ#2236528