ci: bump actions/create-github-app-token from 1 to 2

Bumps [actions/create-github-app-token](https://github.com/actions/create-github-app-token) from 1 to 2.
- [Release notes](https://github.com/actions/create-github-app-token/releases)
- [Commits](https://github.com/actions/create-github-app-token/compare/v1...v2)

---
updated-dependencies:
- dependency-name: actions/create-github-app-token
  dependency-version: '2'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/update-flake.yml

@@ -20,7 +20,7 @@ jobs:
       - uses: DeterminateSystems/nix-installer-action@v16
 
       - id: generate-token
-        uses: actions/create-github-app-token@v1
+        uses: actions/create-github-app-token@v2
         with:
           app-id: ${{ vars.APP_ID }}
           private-key: ${{ secrets.APP_PRIVATE_KEY }}