Remove Auto-Assign workflow

[MSNev]

• copilot needs to be made a collaborator which they won't be

[Copilot]

Pull Request Overview

This PR removes the automated GitHub Actions workflow that assigned Copilot to issues and PRs labeled triage-copilot, since Copilot cannot be added as a collaborator.

• Deletes the copilot-triage-assignment.yml workflow file.
• Eliminates environment variables and labels tied to the auto-assignment process.

Comments suppressed due to low confidence (3)

.github/workflows/copilot-triage-assignment.yml:10

• Remove the COPILOT_USERNAMES repository variable (and any related secrets) now that the workflow is gone to avoid orphaned configuration.

-  COPILOT_USERNAMES: ${{ vars.COPILOT_USERNAMES }}

.github/workflows/copilot-triage-assignment.yml:14

• Consider deleting or deprecating the triage-copilot label since no automation references it anymore.

-    if: ${{ github.event.label.name == 'triage-copilot' }}

.github/workflows/copilot-triage-assignment.yml:1

• Update any contributing guides or team docs to remove mentions of auto-assigning Copilot and describe the new manual triage process.

-name: Assign Copilot to Triage