docs(webhooks-and-event-payloads): 'installation' property is always …

[oscard0m]

Why:

installation and installation_repository payloads have the property installation 100% of the times

Fix #516

What's being changed:

The following payloads have a more accurate description for installation property:

installation

• https://docs.github.com/en/free-pro-team@latest/developers/webhooks-and-events/webhook-events-and-payloads#installation

installation_repositories

• https://docs.github.com/en/free-pro-team@latest/developers/webhooks-and-events/webhook-events-and-payloads#installation_repositories

Check off the following:

• All of the tests are passing.
• I have reviewed my changes in staging. (look for the deploy-to-heroku link in your pull request, then click View deployment)
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[welcome]

Thanks for opening this pull request! A GitHub docs team member should be by to give feedback soon. In the meantime, please check out the contributing guidelines.

[lucascosti]

Thanks a lot for the PR, @dominguezcelada! This looks great, I'll get it merged 🚀

[github-actions]

Thanks very much for contributing! Your pull request has been merged 🎉 You should see your changes appear on the site in approximately 24 hours.