fix: use explicit origin/branch to avoid ambiguous checkout

Author: Algorithm5838

.github/workflows/sync-upstream.yml

@@ -31,7 +31,7 @@ jobs:
 
       - name: Sync main branch
         run: |
-          git checkout main
+          git checkout origin/main -B main
           git merge upstream/main --no-edit || {
             echo "Merge conflict detected on main branch"
             git merge --abort
@@ -47,7 +47,7 @@ jobs:
 
       - name: Sync dev branch
         run: |
-          git checkout dev
+          git checkout origin/dev -B dev
           git merge upstream/dev --no-edit || {
             echo "Merge conflict detected on dev branch"
             git merge --abort