CI: Limit COMMIT_MSG to subject line

Author: effigies

.github/workflows/pythonpackage.yml

@@ -35,6 +35,8 @@ jobs:
         run: |
           if [[ -z "$COMMIT_MSG" ]]; then
             COMMIT_MSG=$(git show -s --format=%s)
+          else
+            COMMIT_MSG=$(echo $COMMIT_MSG | head -n 1)
           fi
           echo $COMMIT_MSG
           echo "commit_message=$COMMIT_MSG" >> $GITHUB_OUTPUT