$ git clone -n https://src.fedoraproject.org/rpms/rust-base64.git /var/lib/mock/f40-build-2034987-47926/root/chroot_tmpdir/scmroot/rust-base64
Cloning into '/var/lib/mock/f40-build-2034987-47926/root/chroot_tmpdir/scmroot/rust-base64'...
$ git fetch origin 0dc17000ec76133b8bef96db2e3d4bae71ae4916:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-base64
 * [new ref]         0dc17000ec76133b8bef96db2e3d4bae71ae4916 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0dc1700 Update to version 0.21.5; Fixes RHBZ#2245633