build(deps): bump FluentAssertions from 6.3.0 to 6.4.0 in /src (#3151)

Bumps [FluentAssertions](https://github.com/fluentassertions/fluentassertions) from 6.3.0 to 6.4.0.
- [Release notes](https://github.com/fluentassertions/fluentassertions/releases)
- [Changelog](https://github.com/fluentassertions/fluentassertions/blob/master/AcceptApiChanges.ps1)
- [Commits](fluentassertions/fluentassertions@6.3.0...6.4.0)

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

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

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

src/Directory.build.props

@@ -48,7 +48,7 @@
     <PackageReference Include="xunit.runner.console" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" />
     <PackageReference Include="Xunit.StaFact" Version="1.0.37" />
-    <PackageReference Include="FluentAssertions" Version="6.3.0" />
+    <PackageReference Include="FluentAssertions" Version="6.4.0" />
     <PackageReference Include="Microsoft.Reactive.Testing" Version="5.0.0" />
     <PackageReference Include="PublicApiGenerator" Version="10.2.0" />
     <PackageReference Include="coverlet.msbuild" Version="3.1.0" PrivateAssets="All" />