Bump guzzlehttp/guzzle from 7.8.1 to 7.9.1 in /graph-tutorial

Bumps [guzzlehttp/guzzle](https://github.com/guzzle/guzzle) from 7.8.1 to 7.9.1.
- [Release notes](https://github.com/guzzle/guzzle/releases)
- [Changelog](https://github.com/guzzle/guzzle/blob/7.9/CHANGELOG.md)
- [Commits](guzzle/guzzle@7.8.1...7.9.1)

---
updated-dependencies:
- dependency-name: guzzlehttp/guzzle
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]