Bump microsoft/microsoft-graph in /app-auth/graphapponlytutorial

Bumps [microsoft/microsoft-graph](https://github.com/microsoftgraph/msgraph-sdk-php) from 2.20.0 to 2.21.0.
- [Release notes](https://github.com/microsoftgraph/msgraph-sdk-php/releases)
- [Changelog](https://github.com/microsoftgraph/msgraph-sdk-php/blob/main/CHANGELOG.md)
- [Commits](microsoftgraph/msgraph-sdk-php@v2.20.0...v2.21.0)

---
updated-dependencies:
- dependency-name: microsoft/microsoft-graph
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]