Add response type attribute code fix places using before license header

### Describe the bug
Given a file with a license header, but no existing usings, the Add Response Type Attribute Code Fix Provider will generate a using statement above the license header.

### To Reproduce
Add license headers to the files in https://github.com/dotnet/aspnetcore/tree/main/src/Mvc/Mvc.Api.Analyzers/test/TestFiles/AddResponseTypeAttributeCodeFixProviderIntegrationTest and then run the tests.