Gitea/Gogs [set repository owner](d644e88107/models/pull.go (L469)) information as Pusher in webhook.
For example, if we have a repository: git.example.com/org1/repo1, owner
of repository will be `org1` and the email field will be empty. This PR
changes gitea/gogs helpers to use the email in Sender field, which is
the user that click the merge button.