$ git clone -n https://src.fedoraproject.org/rpms/blake3.git /var/lib/mock/f41-build-1658846-24203/root/chroot_tmpdir/scmroot/blake3
Cloning into '/var/lib/mock/f41-build-1658846-24203/root/chroot_tmpdir/scmroot/blake3'...
$ git fetch origin 6f637cb961bba9befcd5232f091ff5e5d838207b:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/blake3
 * [new ref]         6f637cb961bba9befcd5232f091ff5e5d838207b -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 6f637cb Build with GCC instead of Clang