Search license also in other branches

[Mte90]

As we can see https://github.com/Mte90/GH-License/blob/817ba6c07b47df89d50b53f9d11aded101cf7c14/ghlicense/repobase.py#L19 we set the default branch. But as today repository can have different as default, like for a fork and so on. We should find for all the repository behind services the "main" branch for a better check.