CI: Log merge contents, not merge itself

Author: ysangkok

.github/workflows/haskell-actions.yml

@@ -39,7 +39,7 @@ jobs:
           fi
           echo $GITHUB_SHA
           git show $GITHUB_SHA
-          for constraint in $(git log "--format=%(trailers:key=New-Versions,valueonly=true)" $GITHUB_SHA -1 --)
+          for constraint in $(git log "--format=%(trailers:key=New-Versions,valueonly=true)" ${GITHUB_SHA}^1 ${GITHUB_SHA}^2)
             do echo "constraints: $constraint" >> cabal.project
           done
           cat cabal.project