fix: Remove required fields that are optional in API responses

[erezrokah]

I already signed the CLA a while back for https://github.com/okta/okta-sdk-golang/pulls?q=is%3Apr+author%3Aerezrokah+is%3Aclosed. I can send it again if you don't have it

Summary

Noticed this while working on #558.
Some fields that were optional in v5 are now required in v6 which fails JSON marshaling. Not sure if this is a problem in the OpenAPI spec or in the code gen, but this PR aims to highlight the marshaling failures that happen in v6, but not in v5.

Type of PR

• Bug Fix (non-breaking fixes to existing functionality)
• New Feature (non-breaking changes that add new functionality)
• Documentation update
• Test Updates
• Other (Please describe the type)

Test Information

• My PR required test updates

Go Version: go version go1.25.4 darwin/arm64
Os Version: MacOS 26.1
OpenAPI Spec Version:

Signoff

• I have submitted a CLA for this PR
• Each commit message explains what the commit does
• I have updated documentation to explain what my PR does
• My code is covered by tests if required
• I ran make fmt on my code
• I did not edit any automatically generated files