actions: use pull_request_target instead of pull_request, use custom fork

[PastaPastaPasta]

Should fix not being able to comment

[UdjinM6]

hmmm... Are you sure?

    if (context.eventName !== 'pull_request') {
      throw new Error(`This action only work with pull_request event not  ${context.eventName}`);
    }

https://github.com/outsideris/potential-conflicts-checker-action/blob/fdecbd447c6399f91d425b8adad1256775727d9d/index.js#L13-L15

EDIT: and official Usage section also mentions pull_request, not pull_request_target

[PastaPastaPasta]

Yeah, you're right.. Need to update the action (there's no reason imo to not allow pull_request_target) see https://github.com/PastaPastaPasta/potential-conflicts-checker-action tag 0.1.1

also see PastaPastaPasta#26 and PastaPastaPasta#25

rebased on using my custom action, uses pull_request_target, and everything is happy

[UdjinM6]

LGTM 👍
utACK