$ git clone -n https://src.fedoraproject.org/rpms/rust-base64.git /var/lib/mock/f39-build-2222945-52713/root/chroot_tmpdir/scmroot/rust-base64
Cloning into '/var/lib/mock/f39-build-2222945-52713/root/chroot_tmpdir/scmroot/rust-base64'...
$ git fetch origin 9acf7ab95cb6bdb52b375957eb58dacbed51290f:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-base64
 * [new ref]         9acf7ab95cb6bdb52b375957eb58dacbed51290f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 9acf7ab Update to version 0.21.6; Fixes RHBZ#2257291