Ensure CI also covers our doctests

[fingolfin]

PR #322 adds a method groebner_basis_with_transform(I::MPolyIdeal; ord::Symbol = :degrevlex, complete_reduction::Bool=false) and also a jldoctest for it ; yet Codecov thinks that function is not covered. That suggests to me that we are either not running the jldoctest as part of our CI; or that if we do so, we are not collecting coverage for it.

This should be checked and resolved.