CI should only run once for either same repo or forked repo

[blrchen]

Currently CI will be triggered by both pull_request and pull_request_target, the result is causing confusion to new contributors.

Ideally, CI should only be fired once for either pull_request for same repo scenario OR pull_request_target for forked repo scenario.

Nice to have but low priority so far.

[blrchen]

@jainr assigning this one to you as you are working on improvements of CI/CD