try newline fix

.github/workflows/matrix-commit-message.yml

@@ -11,7 +11,7 @@ jobs:
           ALL_MSGS=""
           for i in ${{ join(github.event.commits.*.id, ' ') }}; do
             MSG=$(git --no-pager show -s --format='%h %an: %s' $i)
-            ALL_MSGS="$ALL_MSGS$MSG\n"
+            ALL_MSGS="$ALL_MSGS$MSG"$'\n'
           done
           echo "::set-output name=COMMIT_MESSAGE::$ALL_MSGS"
         id: commit-message