feat: restrict to only run for pull_request triggers

[dancamma]

Closes #498

This PR restricts the action to only run for pull_request triggers. For more details, see #355

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[diranged]

This seems like the opposite of the conversation in #355 and #500... whats the motivation to make it even harder to run this on a pull_request_target build? (or frankly any trigger that the repo author feels is valid)?

[simoneb]

@diranged because this predates the conversation we just had and the intent was to make it clearer why the action execution failed. I agree we can refocus the effort on making it work instead.

[diranged]

@diranged because this predates the conversation we just had and the intent was to make it clearer why the action execution failed. I agree we can refocus the effort on making it work instead.

Excellent - thanks, I just saw this come in right now and was confused! :)

[dancamma]

@diranged @simoneb I've just read the update on #355, I'm closing this one