github-gsa: support pull_request_target

[imjasonh]

@k4leung4

i wonder what part of pull_request_target fails to match
a bit more documentation; https://github.com/chainguard-dev/terraform-infra-common/blob/main/modules/github-wif-provider/main.tf#L29-L36

    # assertion.ref has one of the forms:
    #   - Branch: refs/heads/main
    #   - Pull Request: refs/pull/1/merge
    #   - Tag: refs/tags/v1.0.0
    # assertion.workflow_ref has one of the forms:

the issue is likely that pull_request have a refspec of a format of refs/pull/[0-9]+/merge
while pull_request_target has a refspec of a format of refs/heads/main or refs/heads/master
can you file an issue to add support for pull_request_target refspec for github-wif-provider

[mattmoor]

@k4leung4 it looks like the change for this landed?

[aryasoni98]

I came across this issue and would love to contribute could you please assign it to me?

[mattmoor]

I'm pretty sure it's already done, awaiting confirmation.