$ git clone -n https://src.fedoraproject.org/rpms/rust-bytestring.git /var/lib/mock/f40-build-2053857-49096/root/chroot_tmpdir/scmroot/rust-bytestring
Cloning into '/var/lib/mock/f40-build-2053857-49096/root/chroot_tmpdir/scmroot/rust-bytestring'...
$ git fetch origin aab51bd142933df05dae03a24428284a5b258d3f:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-bytestring
 * [new ref]         aab51bd142933df05dae03a24428284a5b258d3f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at aab51bd Update to version 1.3.1; Fixes RHBZ#2246888