ci(studio): use app token for ratchet decrease workflow (#41799)

We're using the default GITHUB_TOKEN to create the ratchet baseline
decrease PR. By default, this does not auto-run the PR checks to prevent
infinite loops.

Switching to a GitHub App token instead so the PR checks will auto-run.

.github/workflows/studio-lint-ratchet-decrease.yml

@@ -35,9 +35,16 @@ jobs:
       - name: Install deps
         run: pnpm install --frozen-lockfile
 
+      - name: Generate token
+        id: app-token
+        uses: actions/create-github-app-token@29824e69f54612133e76f7eaac726eef6c875baf # v2.2.1
+        with:
+          app-id: ${{ secrets.GH_AUTOFIX_APP_ID }}
+          private-key: ${{ secrets.GH_AUTOFIX_PRIVATE_KEY }}
+
       - name: Decrease ESLint ratchet baselines and open PR
         env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GH_TOKEN: ${{ steps.app-token.outputs.token }}
           DEFAULT_BRANCH: ${{ github.event.repository.default_branch }}
         run: |
           set -eo pipefail