When that class represents a commit being pushed to a branch, the list of commits is available and useful to know what was pushed.

When it represents a tag being pushed, the list of commits can be empty. The head_commit comes in handy to know more about the commit.

This change exposes head_commit using the getter getHeadCommit().

The test data already has the data for this to work. The test case has been updated to test for this method.

The docs for this can be found at https://docs.github.com/en/developers/webhooks-and-events/webhooks/webhook-events-and-payloads#push

Fixes: #1585

Description

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