chore(nuget): Bump FluentAssertions from 6.12.0 to 8.7.1

---
updated-dependencies:
- dependency-name: FluentAssertions
  dependency-version: 8.7.1
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: FluentAssertions
  dependency-version: 8.7.1
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: FluentAssertions
  dependency-version: 8.7.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

10xGitHubPolicies.Tests.Contracts/10xGitHubPolicies.Tests.Contracts.csproj

@@ -14,7 +14,7 @@
     <PackageReference Include="xunit" Version="2.9.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
-    <PackageReference Include="FluentAssertions" Version="6.12.0" />
+    <PackageReference Include="FluentAssertions" Version="8.7.1" />
 
     <!-- Contract Testing -->
     <PackageReference Include="NJsonSchema" Version="11.5.1" />