Duplicate job attempts for PR builds causing "Queued — Build Created" problems

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@native-api

Check Settings for your project at Github, the Webhooks and Integrations tabs.

There should be no Travis webhooks, and only one Travis app, “Travis CI”.

Can someone please the Open Source on travis-ci.com - Travis CI documentation?

We followed that to migrate the Python project from travis-ci.org to travis-ci.com, but there was no explanation about webhooks: https://github.com/python/core-workflow/issues/371