Attributes section header is going in the incorrect place

[Eric-Arellano]

For some of the Circuit Library functions, the parameters for the class constructor appear underneath the header "Attributes". This happens in both Sphinx and our repository, such as the 1.3 docs for qiskit.circuit.library.PhaseGate.

Note that these parameters don't have any docstring associated with them. This problem was detected in #2418, which adds parameters with no docstring. Maybe this happens in that specific edge case where there aren't documented parameters?