build(deps): bump fastify from 4.10.2 to 4.26.2 in /test/app

Bumps [fastify](https://github.com/fastify/fastify) from 4.10.2 to 4.26.2.
- [Release notes](https://github.com/fastify/fastify/releases)
- [Commits](fastify/fastify@v4.10.2...v4.26.2)

---
updated-dependencies:
- dependency-name: fastify
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>