Changes made to get_push_commits_event_message in
zerver/lib/webhooks/git.py are common to all Git integrations
that use get_push_commits_event_message. These include github,
github_webhook, gitlab, gogs, bitbucket, bitbucket2. In some
cases (for instance, gitlab), no further changes to gitlab/view.py
will be required to support pushing a local branch without commits;
adding a fixture and tests should suffice.
In cases where the webhook payload doesn't have the username for the
author of a particular commit (this can happen if the author doesn't
have a GitHub account or the author's email is not associated with
their GitHub account), we now use the author's full name to format
messages.
All webhook fixtures in zerver/fixtures/<webhook_name> have now
been moved to dedicated webhook-specific directories under
zerver/webhooks/<webhook_name>/fixtures, where <webhook_name> is
the name of the webhook.
