Allow PRs from forks

[jesusvasquez333]

This resolves #9.

The previous version didn't work when opening PRs from forks due to Github actions running with read-only permissions from forks.

Fortunately, Github recently added a new trigger event pull_request_target which behaves in an almost identical way to the pull_request event, but the action runs in the base of the pull request and will therefore have write permission.

However, as the action runs in the base of the pull request, the pull request number is not available in the environmental variables, which the code was using to extract the number automatically. Therefore, to use this new event, a new input argument was added in order to pass the pull request number which is available in the GitHub context ${{ github.event.pull_request.number }}.

So, for example, to allow PR from forks, in your workflow YAML file you should trigger with:

on:
  pull_request_target:
   types: [opened, labeled, unlabeled, synchronize]

and use these steps (you just need to add the extra pull-request-number input):

uses: jesusvasquez333/verify-pr-label-action@v1.3.1
with:
    github-token: '${{ secrets.GITHUB_TOKEN }}'
    valid-labels: 'bug, enhancement'
    pull-request-number: '${{ github.event.pull_request.number }}'

The changes are backward compatibles, so you can still use the pull_request tigger event, and in that case you don't need to specify the input pull-request-number as you did before. This however won't work with PRs from forks.