Sample code uses outdated @action/toolkit API

[blaxx]

Describe the bug
Workflow action 'create-issue' fails even though, by course description, it should succeed.

To Reproduce
Steps to reproduce the behavior:

1. Follow the course until the end of the 'Add Third Actions JavaScript Files' step
2. Add a label to the current pull request
3. Check your actions tab: the workflow has failed with the error message: 'github.GitHub is not a constructor'

Expected behavior
By adding a label to my pull request I expect the workflow to finish successfully.

Screenshots

Additional context
Seems like the way the octokit client is created in the sample code is no longer supported by @actions/toolkit v3, also see this pull request.

[mattdavis0351]

@blaxx @zhiliangxu Thank you for your contributions to this course. I'll address this issue, and the associate pull requests today 😄