Update CODEOWNER file

[nilo-ms]

Proposed changes

native auth team is the owner native auth scheme and test plan

Type of change

• [ ] Feature work
• [ ] Bug fix
• [ ] Documentation
• [X] Engineering change
• [ ] Test
• [ ] Logging/Telemetry

Risk

• [ ] High – Errors could cause MAJOR regression of many scenarios. (Example: new large features or high level infrastructure changes)
• [ ] Medium – Errors could cause regression of 1 or more scenarios. (Example: somewhat complex bug fixes, small new features)
• [X] Small – No issues are expected. (Example: Very small bug fixes, string changes, or configuration settings changes)