$ git clone -n https://src.fedoraproject.org/rpms/rubygem-posix-spawn.git /var/lib/mock/f41-build-808662-145987/root/chroot_tmpdir/scmroot/rubygem-posix-spawn
Cloning into '/var/lib/mock/f41-build-808662-145987/root/chroot_tmpdir/scmroot/rubygem-posix-spawn'...
$ git fetch origin d15b5eaa87423b634ea1ab292eb254b99dd7d63d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-posix-spawn
 * [new ref]         d15b5eaa87423b634ea1ab292eb254b99dd7d63d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at d15b5ea Fix for C99 compilation (bug 2261664)