Fixes /internal/security/me serverless test (elastic#195846)

## Summary

Replaces the name check with role check. The full name of the user is
different between local and MKI environments.

x-pack/test_serverless/api_integration/test_suites/common/platform_security/authentication.ts

@@ -160,7 +160,7 @@ export default function ({ getService }: FtrProviderContext) {
                 type: 'saml',
               },
               enabled: true,
-              full_name: 'test viewer',
+              roles: [expect.stringContaining('viewer')],
             })
           );
           expect(status).toBe(200);