Bump FluentAssertions from 7.0.0 to 8.6.0

---
updated-dependencies:
- dependency-name: FluentAssertions
  dependency-version: 8.6.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

Directory.Packages.props

@@ -16,7 +16,7 @@
   <!-- Test dependencies -->
   <ItemGroup>
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
-    <PackageVersion Include="FluentAssertions" Version="7.0.0" />
+    <PackageVersion Include="FluentAssertions" Version="8.6.0" />
   </ItemGroup>
   <!-- SourceLink support for all Akka.NET projects -->
   <ItemGroup>