fix: lock FluentAssertions version to 7.x to prevent unintended upgrade (#120)

Author: MrDave1999

Directory.Packages.props

@@ -16,7 +16,7 @@
     <PackageVersion Include="IsExternalInit" Version="1.0.3" />
     <PackageVersion Include="Microsoft.AspNetCore.Mvc.Testing" Version="8.0.0" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
-    <PackageVersion Include="FluentAssertions" Version="6.10.0" />
+    <PackageVersion Include="FluentAssertions" Version="[7.0.0,8.0.0)" />
     <PackageVersion Include="NUnit" Version="3.13.3" />
     <PackageVersion Include="NUnit3TestAdapter" Version="4.3.0" />
     <PackageVersion Include="NUnit.Analyzers" Version="3.5.0" />