Update add-issues-and-prs-to-fs-project-board.yml to use pull_request_target

[BigLep]

Mirror change of filecoin-project/github-mgmt#153

[github-actions]

Before merge, verify that all the following plans are correct. They will be applied as-is after the merge.

Terraform plans

FilOzone

Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
  ~ update in-place

Terraform will perform the following actions:

  # github_repository.this["forge-script-gas-report"] will be updated in-place
  ~ resource "github_repository" "this" {
        id                          = "forge-script-gas-report"
        name                        = "forge-script-gas-report"
        # (36 unchanged attributes hidden)

      ~ security_and_analysis {
          ~ secret_scanning {
              ~ status = "disabled" -> "enabled"
            }
          ~ secret_scanning_push_protection {
              ~ status = "disabled" -> "enabled"
            }
        }
    }

Plan: 0 to add, 1 to change, 0 to destroy.

[github-actions]

The following access changes will be introduced as a result of applying the plan:

Access Changes

There will be no access changes