AAI-236 Exclude empty fields when posting registration data to Auth0 API

[marius-mather]

Description

AAI-236: another small fix encountered when running against the actual Auth0 API: the API doesn't like empty fields being sent as null/None, even if the fields are optional - exclude these fields when posting data

Changes

• Use exclude_none=True so None fields are not included in posted data

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added unit / integration tests that prove my fix is effective or that my feature works
• I have run all tests locally and they pass
• I have updated the documentation (if applicable)

How to Test Manually (if necessary)

Run uv run pytest

[amandazhuyilan]

Nice one!