Improve GitHub client message when it's failed

[sivchari]

What would you like to be added:

The event-watcher pushes a commit to main branch of GitHub when event is registered by someone. But if the repository prohibit to do push, this event will be failed. Then, the event-watcher returned ErrBranchNotFresh. The message is wrong and developers is confused as to why is this branch isn't fresh. I propose a 2 way. the one is piped returns more clearly message. In the other hand, piped uses GitHub client (e.g. google/go-github). wdyt ?

Why is this needed:

More clearly error message.

[hungran]

@sivchari um not sure how can make massage more clearly when doesn't have permission to push, in almost cases, will return error: failed to push some refs to +1 if we can consider to use go-github