chore: add explicit permissions to release-please workflow

[kinyoklion]

Summary

Adds explicit contents: write and pull-requests: write permissions to the release-please job. These are required for the release-please action to create release PRs and GitHub releases. Without explicit permissions, the job relies on the repository/org default GITHUB_TOKEN permissions, which may be insufficient if defaults are tightened to read-only.

Downstream jobs (release-client, release-server, provenance, etc.) already have their own explicit permissions blocks and are unaffected by this change.

Review & Testing Checklist for Human

• Verify no other implicit permissions are needed by the release-please job. Adding an explicit job-level permissions block restricts the token to only the listed permissions, revoking any previously inherited defaults. If the release-please action in this repo needs anything beyond contents and pull-requests (e.g., id-token: write), it will break.
• After merging, monitor the next release-please workflow run (triggered by a push to main) to confirm it still creates/updates release PRs successfully.

Notes

This is part of a batch update across all launchdarkly-sdk-tagged repositories whose release-please workflows were missing explicit permissions on their default branch.

Link to Devin session: https://app.devin.ai/sessions/a83b6e4f4fa14b96b859cfb50755a2c1
Requested by: @kinyoklion

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Note

Low Risk
Low risk configuration change, but it can break releases if release-please requires additional permissions beyond contents and pull-requests under restricted tokens.

Overview
Hardens the release-please GitHub Actions workflow by adding an explicit job-level permissions block for release-please (contents: write and pull-requests: write).

This removes reliance on repository/org default GITHUB_TOKEN permissions and ensures the job can create/update release PRs and GitHub releases when defaults are tightened.

^{Written by Cursor Bugbot for commit 16f70bb. This will update automatically on new commits. Configure here.}

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