build(deps): bump FluentAssertions from 5.10.3 to 6.0.0 in /src (#748)

Bumps [FluentAssertions](https://github.com/fluentassertions/fluentassertions) from 5.10.3 to 6.0.0.
- [Release notes](https://github.com/fluentassertions/fluentassertions/releases)
- [Changelog](https://github.com/fluentassertions/fluentassertions/blob/master/AcceptApiChanges.ps1)
- [Commits](fluentassertions/fluentassertions@5.10.3...6.0.0)

---
updated-dependencies:
- dependency-name: FluentAssertions
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

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

src/Directory.build.props

@@ -38,7 +38,7 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.11.0" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="Xunit.StaFact" Version="1.0.37" />
-    <PackageReference Include="FluentAssertions" Version="5.10.3" />
+    <PackageReference Include="FluentAssertions" Version="6.0.0" />
     <PackageReference Include="Microsoft.Reactive.Testing" Version="5.0.0" />
     <PackageReference Include="PublicApiGenerator" Version="10.2.0" />
     <PackageReference Include="DiffEngine" Version="7.1.0" />