fix(sync): detect add-add merge conflicts

Author: tae898

sync-upstream.sh

@@ -33,7 +33,7 @@ PROTECTED_SOURCE_REV=""
 
 try_auto_resolve() {
     local conflicts resolved path handled
-    conflicts=$(git status --porcelain | awk '$1 ~ /U/ {print $2}')
+    conflicts=$(git diff --name-only --diff-filter=U)
     if [ -z "$conflicts" ]; then
         return 1
     fi