Fix 'PolicyPlatformOperatingSystemType': OSX -> MACOS + adding CHROMEOS

[dparolla]

Summary

Obvious Fix:
Fixes a bug when trying to read a policy rule with "MacOs" or "ChromeOS" platform condition.
Current error:
Failed to unmarshal ListPolicyRules200ResponseInner as AccessPolicyRule: MACOS is not a valid PolicyPlatformOperatingSystemType

Fixes #
N/A

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:
Os Version:
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

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