$ git clone -n https://src.fedoraproject.org/rpms/rust-av1-grain.git /var/lib/mock/f39-build-2232735-53344/root/chroot_tmpdir/scmroot/rust-av1-grain
Cloning into '/var/lib/mock/f39-build-2232735-53344/root/chroot_tmpdir/scmroot/rust-av1-grain'...
$ git fetch origin b3e1b1727775ac6d46981c20c8f0aadf2d8e4686:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-av1-grain
 * [new ref]         b3e1b1727775ac6d46981c20c8f0aadf2d8e4686 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b3e1b17 Update to version 0.2.3; Fixes RHBZ#2256765