Certain Organization Policy managed constraints that were released were not functioning as intended

## Fix Certain Organization Policy [managed constraints](https://cloud.google.com/resource-manager/docs/organization-policy/overview#managed-constraints) that were released on August 21, 2025 were not functioning as intended. The Organization Policy Service evaluated these constraints as if the `effectiveInstanceMetadata` field of the resources that they were enforced on was empty, causing them to always evaluate to either allow or deny access to the resource. The following managed constraints were evaluated to always allow creation of resources where they were enforced: * `constraints/compute.managed.disableGuestAttributesAccess` * `constraints/compute.managed.disableSerialPortAccess` * `constraints/compute.managed.disableSerialPortLogging` The following managed constraints were evaluated to always block creation of resources where they were enforced: * `constraints/compute.managed.disallowGlobalDns` * `constraints/compute.managed.requireOsConfig` * `constraints/compute.managed.requireOsLogin` This issue has been corrected, and these constraints now properly evaluate the `effectiveInstanceMetadata` field to determine whether resource creation should be allowed or blocked.