Add pull request target to bc lint (#106065)
In order to get around the approval needed for first time contributors, add pull_request_target trigger for bc lint like for check labels.
Documentation about approvals here https://docs.github.com/en/actions/managing-workflow-runs/approving-workflow-runs-from-public-forks specifically:
> Note: Workflows triggered by pull_request_target events are run in the context of the base branch. Since the base branch is considered trusted, workflows triggered by these events will always run, regardless of approval settings. For more information about the pull_request_target event, see "[Events that trigger workflows](https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#pull_request_target)."
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106065
Approved by: https://github.com/huydhn, https://github.com/malfet
