Guard Rivendell Council workflow against fork PR write-permission failures

[Copilot]

Description

On pull_request events from forks, GITHUB_TOKEN is read-only — the council job requesting pull-requests: write would fail for external contributors. Adds a job-level guard to skip execution on fork PRs.

Changes

• .github/workflows/rivendell_council.yml: Added if condition to the council job:

  if: github.event.pull_request.head.repo.full_name == github.repository

  The job is now skipped entirely when the PR originates from a fork, avoiding token permission errors.

Type of change

• This pull request is a minor refactor, code cleanup, test improvement, or other maintenance task and doesn't change the functionality of Radius (issue link optional).

Contributor checklist

• An overview of proposed schema changes is included in a linked GitHub issue.
  • Yes
  • Not applicable
• A design document PR is created in the design-notes repository, if new APIs are being introduced.
  • Yes
  • Not applicable
• The design document has been reviewed and approved by Radius maintainers/approvers.
  • Yes
  • Not applicable
• A PR for the samples repository is created, if existing samples are affected by the changes in this PR.
  • Yes
  • Not applicable
• A PR for the documentation repository is created, if the changes in this PR affect the documentation or any user facing updates are made.
  • Yes
  • Not applicable
• A PR for the recipes repository is created, if existing recipes are affected by the changes in this PR.
  • Yes
  • Not applicable

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