Add raw tags for issue_comment example

[lucascosti]

Why:

Fixes: #1096

A code block had Actions context examples, but were being stripped out when rendering because of the Liquid processing. This PR adds raw tags around the code block so that they won't be processed.

Stage preview: https://docs-1373--lucascostiissue-com.herokuapp.com/en/free-pro-team@latest/actions/reference/events-that-trigger-workflows#issue_comment

Check off the following:

• All of the tests are passing.
• I have reviewed my changes in staging.
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[martin389]

Thanks for adding this! 🚀

[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.