Always fill out PR title after conflict resolution

[webknjaz]

Before this change, cherry-picker used to loose the backported commit message and didn't pass anything to the push_to_remote() method which resulted in sending an API request to GitHub that had an empty title upon resume. This caused GitHub respond with an error.

This code path was only problematic for people having a GitHub token in their env and therefore enjoying the benefits of the PR autocreation.

After this change, cherry-picker picks up the commit message correctly and extracts the proper PR title and body out of it.

[webknjaz]

@sivel this should fix your problem :point_up:

[webknjaz]

Please ignore the nightly job, its failure is unrelated to this change. It happens because pytest turns all warnings into errors.

[sivel]

I've confirmed this fixes my issue.

Instead of:

422
{"message":"Validation Failed","errors":[{"resource":"Issue","code":"missing_field","field":"title"}],"documentation_url":"https://docs.github.com/rest/reference/pulls#create-a-pull-request"}

The PR is properly created.