Add LockMembershipsToSAML support to Application Settings

Overview

The lock_memberships_to_saml attribute was missing from both the Settings and UpdateSettingsOptions structs, leaving users unable to read or update this setting through the client. This MR adds the missing field and the corresponding tests to ensure correct behavior.

Changes

settings.go

• Added LockMembershipsToSAML to the Settings struct
• Added LockMembershipsToSAML to the UpdateSettingsOptions struct
• Fixed url tag that was incorrectly added to LockMembershipsToSAML in the Settings struct — response structs use json tags only

settings_test.go

• Added TestGetSettings_LockMembershipsToSAML to verify the field is correctly read from the API response
• Added TestUpdateSettings_LockMembershipsToSAML to verify the field is correctly sent in the request body

References

• #2237 (closed)
• Application Settings API | GitLab Docs