chore(deps): update dependency nsubstitute to v6

Author: renovate[bot]

test/Directory.Build.props

@@ -20,7 +20,7 @@
     <PackageReference Include="AwesomeAssertions" Version="9.4.0" />
     <PackageReference Include="coverlet.msbuild" Version="10.0.1" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
-    <PackageReference Include="NSubstitute" Version="5.3.0" />
+    <PackageReference Include="NSubstitute" Version="6.0.0" />
     <PackageReference Include="xunit.v3" Version="3.2.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
       <PrivateAssets>all</PrivateAssets>