CI (Buildbot): Fix a bug in the "Create Pending Statuses" GitHub Actions workflow (#41815)

Author: DilumAluthge

.github/workflows/statuses.yml

@@ -50,10 +50,10 @@ jobs:
       fail-fast: false
     steps:
       - run: echo "SHA=${{ github.event.pull_request.head.sha }}" >> $GITHUB_ENV
-        if: github.event_name == 'pull_request'
+        if: github.event_name == 'pull_request_target'
 
       - run: echo "SHA=${{ env.GITHUB_SHA }}" >> $GITHUB_ENV
-        if: github.event_name != 'pull_request'
+        if: github.event_name != 'pull_request_target'
 
       - run: echo "The SHA is ${{ env.SHA }}"