$ git clone -n https://src.fedoraproject.org/rpms/ruby.git /var/lib/mock/f42-build-3272206-41305/root/chroot_tmpdir/scmroot/ruby
Cloning into '/var/lib/mock/f42-build-3272206-41305/root/chroot_tmpdir/scmroot/ruby'...
$ git fetch origin 74a9a07c691dd161a56211930c06e168d4bf9e85:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/ruby
 * [new ref]         74a9a07c691dd161a56211930c06e168d4bf9e85 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 74a9a07 Fix `gem install` to generate documentation