CI: Don't include merge commits when checking message length.

.github/workflows/ci.yml

@@ -61,7 +61,7 @@ jobs:
     - name: Check commit message
       run: |
         # Get last commit message
-        git log -1 --pretty=format:"%s" | grep -c "^[^#].{78}"
+        git log -1 --pretty=format:"%s" --no-merges | grep -c "^[^#].{78}"
         if [ $? -eq 0 ]; then
           echo "Last commit log contains a line with more than 78 characters."
           exit 1