Allow the GitCommandWrapperType definition to be used within the Repoclassmethods. This change follows the intended purpose as stated inthe code, "Subclasses may easily bring in their own custom types byplacing a constructor or type here."The usecase that prompted this change has to do with`GIT_SSH_COMMAND`. The goal is to setup a custom `Git` class withknowledge of the value, something like as follows```pythonfrom git import Git as BaseGit, Repo as BaseRepoclass Git(BaseGit):    def __init__(self, *args, **kwargs):        super().__init__(*args, **kwargs)        # For example, assign the SSH command using the current flask        # app's configured setting.        self.update_environment(GIT_SSH_COMMAND=current_app.config['GIT_SSH_COMMAND'])class Repo(BaseRepo):    GitCommandWrapperType = _Git```With this change, the above example will allow the developer to use`Repo.clone_from(...)` with the indended outcome. Otherwise thedeveloper will have two differing result when using `Repo(...)` vs`Repo.clone_from(...)`.