Update dependency FluentAssertions to v6.8.0 (#568)

+semver:patch

Author: renovate[bot]

src/FluentNHibernate.Specs/FluentNHibernate.Specs.csproj

@@ -11,7 +11,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
-    <PackageReference Include="FluentAssertions" Version="6.7.0" />
+    <PackageReference Include="FluentAssertions" Version="6.8.0" />
     <PackageReference Include="Machine.Specifications" Version="1.1.0" />
     <PackageReference Include="Machine.Specifications.Runner.VisualStudio" Version="2.10.2" />
   </ItemGroup>