Bump NUnit3TestAdapter from 4.5.0 to 4.6.0 in /docs/core/testing/snippets/order-unit-tests/csharp in the dotnet group

Bump NUnit3TestAdapter from 4.5.0 to 4.6.0 in /docs/core/testing/snippets/order-unit-tests/csharp in the dotnet group #1211