f0d46cdd doc: fix typo in filename data_assembly.md

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Reviewed-by: Christos Tsolakis <christos.tsolakis@kitware.com>
Acked-by: Sean Ahern <sean.ahern@ansys.com>
Merge-request: !11913