[calc_sum](https://sphinx-needs.readthedocs.io/en/latest/dynamic_functions.html#sphinx_needs.functions.common.calc_sum) does not provide the needs in scope to the filter function, so we cannot use them in the calc_sum filter string. You can see in current [source](https://github.com/useblocks/sphinx-needs/blob/c25df13fd903bfbcf20bab3fccbdd09ec4e1ab2e/sphinx_needs/functions/common.py#L386) that we miss to pass `check_needs` as parameter to `filter_single_need`.
