Allow to filter builds by event type

[simleo]

It would be useful to add a "filter-by-event-type" (e.g., push, pull request, ...) feature to our API endpoint for getting test builds. A common use case would be to filter out PR builds, since they're more likely to fail while the PR is being fine-tuned. PyGithub's WorkflowRun objects have an event attribute that should do the trick (values can be push, pull_request, etc.), at least for GitHub builds.