Update dependency FluentAssertions to v8 (#15)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

src/Directory.Packages.props

@@ -14,7 +14,7 @@
     <PackageVersion Include="xunit.runner.console" Version="2.9.3" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="2.8.2" />
     <PackageVersion Include="Xunit.StaFact" Version="1.2.69" />
-    <PackageVersion Include="FluentAssertions" Version="6.12.2" />
+    <PackageVersion Include="FluentAssertions" Version="8.8.0" />
     <PackageVersion Include="Microsoft.Reactive.Testing" Version="6.1.0" />
     <PackageVersion Include="PublicApiGenerator" Version="11.5.3" />
     <PackageVersion Include="coverlet.msbuild" Version="6.0.4" />