chore: update node.js to v26 (#38285)

- bump ci, flake and `@types/node` to node 26
- regenerate flake.lock which is needed for that package
- refactor workflow to use shared composite action

.github/workflows/pull-labeler.yml

@@ -35,7 +35,7 @@ jobs:
           ref: ${{ github.event.pull_request.base.sha }}
       - uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
         with:
-          node-version: 24
+          node-version: 26
       # Labels are only synced after the title lints, so an invalid title never reaches the label diff.
       - run: node ./tools/ci-tools.ts lint-pr-title
         env: