Fix automatic version detection after tagging 3.13.0

Our build system version detection is based on assumption that all
repos either have same tag at HEAD, or not. If some repos have a tag,
and others - don't, build aborts. To prevent build issues after
adding commits to some (but not all) repos, we add this empty commit.

Changelog: None

Signed-off-by: Aleksei Shpakovskii <aleksei.shpakovskii@cfengine.com>

Author: Aleksei Shpakovskii