Use :match-dynamic for helm-org-ql source

I was looking through docstring for :candidates option in helm sources:

> This function, generally should not compute candidates according to
> `helm-pattern' which defeat all the Helm's matching mechanism
> i.e. multiple pattern matching and/or fuzzy matching.
> If you want to do so, use :match-dynamic slot to be sure matching
> occur only in :candidates function and there is no conflict with
> other match functions.

Probably, it should be set in `helm-org-ql-source`.