chore: add FluentAssertions nuget package to test projects (dotnet#8946)

Add FluentAssertions package to test projects

Author: filzrev

Directory.Packages.props

@@ -37,6 +37,7 @@
 
     <!-- Test only -->
     <PackageVersion Include="coverlet.collector" Version="6.0.0" />
+    <PackageVersion Include="FluentAssertions" Version="6.11.0" />
     <PackageVersion Include="Magick.NET-Q16-AnyCPU" Version="13.1.3" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.6.3" />
     <PackageVersion Include="Microsoft.Playwright" Version="1.35.0" />

test/Directory.Build.props

@@ -14,6 +14,7 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
+    <PackageReference Include="FluentAssertions" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" />
     <!--
       The NuGet.Frameworks package is required to run csproj based tests targeting .NET 7.0.200.