$ git clone -n https://src.fedoraproject.org/rpms/R-bookdown.git /var/lib/mock/f40-build-1930462-25111/root/chroot_tmpdir/scmroot/R-bookdown
Cloning into '/var/lib/mock/f40-build-1930462-25111/root/chroot_tmpdir/scmroot/R-bookdown'...
$ git fetch origin 3ed7f719496554d760a206cf125d6ced9ebe203f:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-bookdown
 * [new ref]         3ed7f719496554d760a206cf125d6ced9ebe203f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3ed7f71 R-maint-sig mass rebuild