$ git clone -n https://src.fedoraproject.org/rpms/rust-cfg-expr.git /var/lib/mock/f39-build-2186817-51375/root/chroot_tmpdir/scmroot/rust-cfg-expr
Cloning into '/var/lib/mock/f39-build-2186817-51375/root/chroot_tmpdir/scmroot/rust-cfg-expr'...
$ git fetch origin 1f4e556f3aefe8eb5aae51ff6a0e93a938c742ff:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-cfg-expr
 * [new ref]         1f4e556f3aefe8eb5aae51ff6a0e93a938c742ff -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 1f4e556 Update to version 0.15.6; Fixes RHBZ#2256441