$ git clone -n https://src.fedoraproject.org/rpms/rust-serde_json.git /var/lib/mock/f40-build-2150865-50900/root/chroot_tmpdir/scmroot/rust-serde_json
Cloning into '/var/lib/mock/f40-build-2150865-50900/root/chroot_tmpdir/scmroot/rust-serde_json'...
$ git fetch origin 725068a93db5bd32cd03d66c45771db345e852d7:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-serde_json
 * [new ref]         725068a93db5bd32cd03d66c45771db345e852d7 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 725068a Update to version 1.0.108; Fixes RHBZ#2247101