ci(project): use ohmyzsh's bot credentials

.github/workflows/project.yml

@@ -15,9 +15,15 @@ jobs:
     name: Add to project
     runs-on: ubuntu-latest
     if: github.repository == 'ohmyzsh/ohmyzsh'
-    env:
-      GITHUB_TOKEN: ${{ secrets.PROJECT_TOKEN }}
     steps:
+      - name: Authenticate as @ohmyzsh
+        id: generate_token
+        uses: ohmyzsh/github-app-token@v2
+        with:
+          app_id: ${{ secrets.OHMYZSH_APP_ID }}
+          private_key: ${{ secrets.OHMYZSH_APP_PRIVATE_KEY }}
+      - name: Store app token
+        run: echo "GH_TOKEN=${{ steps.generate_token.outputs.token }}" >> "$GITHUB_ENV"
       - name: Read project data
         env:
           ORGANIZATION: ohmyzsh