chore: update librarian to v0.31.0

[zhumin8]

Update librarian version and re-generate.
Run with commands:

go run github.com/googleapis/librarian/cmd/librarian@latest update version
V=$(go run github.com/googleapis/librarian/cmd/librarian@latest config get version)
go run github.com/googleapis/librarian/cmd/librarian@${V} tidy
# Build a new Docker image
go run github.com/googleapis/librarian/tool/cmd/builddockerimages@latest --language python --version=${V}
# Regenerate all libraries in Docker. Around 2 minutes.
docker run -u $(id -u):$(id -g) -v .:/repo -v ~/.cache:/.cache -w /repo docker.io/library/librarian-python:${V}  generate -v --all

[gemini-code-assist]

Code Review

This pull request updates the version in librarian.yaml from v0.30.0 to v0.31.0. There are no review comments, and I have no feedback to provide.