Enable org-billed Copilot auth for agentic workflows

[Copilot]

This updates the repository’s agentic workflows to use the current Copilot permission model for org-wide billing. The workflows no longer depend on the legacy COPILOT_GITHUB_TOKEN secret path for Copilot inference.

• Workflow source updates

  • Updated the agentic workflow frontmatter in:
    • .github/workflows/bump-tcgc-csharp.md
    • .github/workflows/issue-triage.md
  • Replaced broad read-all shorthand with explicit permissions that preserve read access while enabling Copilot requests:

    permissions:
      all: read
      copilot-requests: write

• Generated workflow refresh

  • Recompiled the corresponding .lock.yml files so generated workflows match the new auth model.
  • The generated workflows now use github.token for Copilot auth instead of the old secret-validation flow.

• Behavioral impact

  • Removes reliance on the previous Copilot token setup for these agentic workflows.
  • Aligns workflow auth with the current org-billed Copilot execution path.