$ git clone -n https://src.fedoraproject.org/rpms/rust-serde_json.git /var/lib/mock/f40-build-2233949-53387/root/chroot_tmpdir/scmroot/rust-serde_json
Cloning into '/var/lib/mock/f40-build-2233949-53387/root/chroot_tmpdir/scmroot/rust-serde_json'...
$ git fetch origin 3a05d52699a5455e7a46e2469aa7c2fac632301e:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-serde_json
 * [new ref]         3a05d52699a5455e7a46e2469aa7c2fac632301e -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3a05d52 Update to version 1.0.111; Fixes RHBZ#2256728