$ git clone -n https://src.fedoraproject.org/rpms/rubygem-posix-spawn.git /var/lib/mock/f45-build-35159-693/root/chroot_tmpdir/scmroot/rubygem-posix-spawn
Cloning into '/var/lib/mock/f45-build-35159-693/root/chroot_tmpdir/scmroot/rubygem-posix-spawn'...
$ git fetch origin 8e6e803be78cc3eb560e5142c815b44c21cc6c6a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-posix-spawn
 * [new ref]         8e6e803be78cc3eb560e5142c815b44c21cc6c6a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 8e6e803 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild