$ git clone -n https://src.fedoraproject.org/rpms/rust-jpeg-decoder.git /var/lib/mock/f39-build-1521891-35867/root/chroot_tmpdir/scmroot/rust-jpeg-decoder
Cloning into '/var/lib/mock/f39-build-1521891-35867/root/chroot_tmpdir/scmroot/rust-jpeg-decoder'...
$ git fetch origin ab4f0856f70e089b8e68ad1933c50ea48b3588b2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-jpeg-decoder
 * [new ref]         ab4f0856f70e089b8e68ad1933c50ea48b3588b2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ab4f085 Update to version 0.3.0; Fixes RHBZ#2135555