[TODO] Don't pre-authenticate installation removed event

[webknjaz]

[webknjaz]

Implementation instruction: #49 (comment).

[webknjaz]

In the past, we've had to do something similar for events that lack the 'installation' key:

• 94e7765
• sanitizers/chronographer-github-app@4618014
• not all events have 'installation' #27

[webknjaz]

Implementation instruction: #49 (comment).

Action items:

• Here https://github.com/sanitizers/octomachinery/blob/3ce9e19/octomachinery/github/api/app_client.py#L110 add something like or (event.name == 'installation' and event.payload['action'] == 'deleted')
• Figure out if installation.suspend should (always) be treated the same: https://docs.github.com/developers/webhooks-and-events/webhooks/webhook-events-and-payloads?actionType=suspend#installation
• Test the above