Quickstart: check if action is run in context of template repository by looking at github.event.repository.template_repository

[gr2m]

Why:

Checking for github.event.repository.template_repository makes it work for all courses, not only githublearn/* repositories

What's being changed:

Just a suggestion. But I think this makes it more generic?

I originally thought the expression was incorrect because on https://githublearn.github.io/.github/quickstart it only shows

    if: $

But that seems to be an unrelated rendering problem?

Check off the following:

• For workflow changes, I have verified the Actions workflows function as expected.
• For content changes, I have reviewed the style guide.

[heiskr]

Thanks for noticing this issue 🎉 This file now lives in github.com/github/skills and I've added {% raw %} to address the rendering issue, and it now appropriately checks is_template :)