sync-fork: pass --no-rebase to git pull to fix divergent branch error

Co-Authored-By: Claude <noreply@anthropic.com>

Author: koki-develop

.github/workflows/sync-fork.yml

@@ -25,5 +25,5 @@ jobs:
       - name: Pull upstream changes
         run: |
           git remote add upstream https://github.com/google/nsjail.git
-          git pull upstream master
+          git pull --no-rebase upstream master
           git push origin master