Update NUnit3TestAdapter from 5.2.0 to 6.0.0 in Documentation.Tests

Co-authored-by: Romfos <12048821+Romfos@users.noreply.github.com>

Author: Copilot

tests/NSubstitute.Documentation.Tests/NSubstitute.Documentation.Tests.csproj

@@ -9,7 +9,7 @@
 
   <ItemGroup>
     <PackageReference Include="NUnit" Version="4.4.0" />
-    <PackageReference Include="NUnit3TestAdapter" Version="5.2.0" />
+    <PackageReference Include="NUnit3TestAdapter" Version="6.0.0" />
   </ItemGroup>
 
   <ItemGroup>