chore(deps): update dependency fluentassertions to 8.4.0

Author: renovate[bot]

src/Directory.Build.props

@@ -49,7 +49,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
-    <PackageReference Include="FluentAssertions" Version="8.3.0" />
+    <PackageReference Include="FluentAssertions" Version="8.4.0" />
     <PackageReference Include="ReactiveUI.Testing" Version="20.4.1" />
   </ItemGroup>