devel/rubygem-google-apis-cloudbilling_v1: update to 0.40.0
Required for gitlab 19.4.
Changes: https://github.com/googleapis/google-api-ruby-client/blob/main/generated/google-apis-cloudbilling_v1/CHANGELOG.md
(cherry picked from commit cb8676d837900e5410f81a1aa8bcfad7798f3674)