fix(python): id token write added to root

[andrewklatzke]

Adds the id-token:write permission to the root workflow

---

Note

Overview
Adds id-token: write to the release-please job in release-please.yml, alongside the existing contents: write and pull-requests: write permissions.

This aligns the root automated release job with the publish jobs that already request OIDC tokens, so GitHub Actions can mint ID tokens where the workflow or release-please step needs them.

^{Reviewed by Cursor Bugbot for commit 9e75735. Bugbot is set up for automated code reviews on this repo. Configure here.}