Support for pull_request_target event

[Dasch0]

Hello,

First off, this is an excellent script and has been a huge help to me. However I ran into a small issue on GitHub's end when using it.

The pull_request event has a number of limitations for use with Github actions, especially regarding pull requests from forked repositories. This is described in detail in the link below:
https://git.luolix.topmunity/t/github-actions-are-severely-limited-on-prs/18179

As a fix, Github recently added the pull_request_target event type, which fixes all of the issues described above. Documentation for pull_request_target is shown below:
https://docs.github.com/en/actions/reference/events-that-trigger-workflows#pull_request_target

This event behaves almost exactly the same as pull_request as far as this script is concerned. In fact if the error checking is changed to allow for pull_request_target as the event type, this script works properly as is. See a proof of concept in this fork:

https://github.com/silabs-DavidS/close-pull-request-target

As this repo is the top result on the marketplace for closing pull requests, I think a new release that allows for the pull_request_target event would be great to have.

Best,
David

[superbrothers]

@Dasch0 I've changed to use pull_request_target event instead, and released v3.0.0. Thank you so much for your comment!