chore(deps): bump @octokit/app from 14.1.0 to 15.1.3

Bumps [@octokit/app](https://github.com/octokit/app.js) from 14.1.0 to 15.1.3.
- [Release notes](https://github.com/octokit/app.js/releases)
- [Commits](octokit/app.js@v14.1.0...v15.1.3)

---
updated-dependencies:
- dependency-name: "@octokit/app"
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]