Remove checkout the PR sha from danger-pr.yml (#54904)

Summary:
This PR reverts a change marked unsecure by our security team

## Changelog:
[Internal] -

Pull Request resolved: #54904

Test Plan: N/A

Reviewed By: yungsters

Differential Revision: D89306739

Pulled By: cipolleschi

fbshipit-source-id: 0bd994d02f5971a66a0c43e8121acc7c05a66869

Author: cipolleschi

.github/workflows/danger-pr.yml

@@ -19,8 +19,6 @@ jobs:
     steps:
       - name: Check out PR branch
         uses: actions/checkout@v6
-        with:
-          ref: ${{ github.event.pull_request.head.sha }}
       - name: Setup Node.js
         uses: ./.github/actions/setup-node
       - name: Run yarn install