Bump NUnit (#2300)

Bumps the dotnet group in /docs/testing/snippets/testing/nunit/AspireApp.Tests with 1 update: [NUnit](https://github.com/nunit/nunit).


Updates `NUnit` from 4.2.2 to 4.3.0
- [Release notes](https://github.com/nunit/nunit/releases)
- [Changelog](https://github.com/nunit/nunit/blob/main/CHANGES.md)
- [Commits](nunit/nunit@4.2.2...4.3.0)

---
updated-dependencies:
- dependency-name: NUnit
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: dotnet
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>