fix: use sha instead of ref when marking on pull request

Author: Oleg

.github/workflows/build.yml

@@ -69,7 +69,7 @@ jobs:
 
     env:
       TAG: v${{ needs.meta.outputs.latest-version }}
-      COMMIT: ${{ github.event.pull_request.base.ref || github.event.before }} # either the PR base ref or previous commit in the branch
+      COMMIT: ${{ github.event.pull_request.base.sha || github.event.before }} # either the PR base ref or previous commit in the branch
       GH_REPOSITORY: ${{ github.repository }}
 
     steps: