build(deps): bump mdast-util-to-hast in /examples/github-app (#3650)

Bumps [mdast-util-to-hast](https://github.com/syntax-tree/mdast-util-to-hast) from 13.0.2 to 13.2.1.
- [Release notes](https://github.com/syntax-tree/mdast-util-to-hast/releases)
- [Commits](syntax-tree/mdast-util-to-hast@13.0.2...13.2.1)

---
updated-dependencies:
- dependency-name: mdast-util-to-hast
  dependency-version: 13.2.1
  dependency-type: indirect
...

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