Support head_commit for GHEventPayload.Push

[rahulsom]

Describe the bug
The GitHub specification for that type offers a field called head_commit. The class GHEventPayload.Push does not have that field.

To Reproduce
Steps to reproduce the behavior:

1. See the source for GHEventPayload.Push.

Expected behavior
That field should exist with the type PushCommit.

Desktop (please complete the following information):

• Version 1.313

Additional context

[rahulsom]

The docs in https://docs.github.com/en/developers/webhooks-and-events/webhooks/webhook-events-and-payloads#push show the field.