Auto merge of #12508 - weihanglo:ci-github-sha, r=ehuss

ci: use pull request head commit whenever possible

Author: bors

.github/workflows/main.yml

@@ -87,7 +87,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       BASE_SHA: ${{ github.event.pull_request.base.sha }}
-      HEAD_SHA: ${{ github.sha }}
+      HEAD_SHA: ${{ github.event.pull_request.head.sha != '' && github.event.pull_request.head.sha || github.sha  }}
     steps:
       - uses: actions/checkout@v3
         with: