Add missing environment and label check to triage workflow - #12706

Restores two configurations that were inadvertently removed during the migration to shared workflows in #12677:

• environment: cli-discuss-automation — Required for the discuss job to access CLI_DISCUSSION_TRIAGE_TOKEN when creating internal issues in github/cli
• Label name check — Adds github.event.label.name == 'discuss' to the job condition to prevent triggering on unrelated labels

jobs:
  discuss:
    if: github.event.action == 'labeled' && github.event.label.name == 'discuss'
    environment: cli-discuss-automation
    uses: desktop/gh-cli-and-desktop-shared-workflows/.github/workflows/triage-discuss.yml@main

Without these, the workflow would either fail authentication or run unnecessarily on every labeled event.

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