Enable note migration by resolving correct response

[codemonium]

Prior to this change, we would ignore the

await this.githubApi.pulls.create(props);

return value, which is the actual Pull Request data. As a result, none of the logic beyond creating the Pull Request could run: https://github.com/piceaTech/node-gitlab-2-github/blob/master/src/githubHelper.ts#L792

It looks like https://github.com/piceaTech/node-gitlab-2-github/commit/d65ac3f72f02ed5b670e847e278d4c736a7f5f1a caused this issue, but I'm not sure if my solution causes a regression.