$ git clone -n https://src.fedoraproject.org/rpms/rust-proc-mounts.git /var/lib/mock/f39-build-1564484-37504/root/chroot_tmpdir/scmroot/rust-proc-mounts
Cloning into '/var/lib/mock/f39-build-1564484-37504/root/chroot_tmpdir/scmroot/rust-proc-mounts'...
$ git fetch origin 83b8d3589f72511180bf53a6a991fcb9e8798b72:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-proc-mounts
 * [new ref]         83b8d3589f72511180bf53a6a991fcb9e8798b72 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 83b8d35 Update to version 0.3.0; Fixes RHBZ#2066343