fix(ci): target fork repo explicitly in upstream-sync PR creation

Without --repo flag, gh inferred upstream repo from branch origin,
causing PR creation to fail with permission errors.
🤖 Generated with [Nori](https://nori.ai)

Co-Authored-By: Nori <noreply@tilework.tech>

Author: CSRessel

.github/workflows/upstream-sync.yml

@@ -258,6 +258,7 @@ jobs:
             echo "$pr_body"
           else
             gh pr create \
+              --repo "${{ github.repository }}" \
               --base dev \
               --head "$SYNC_BRANCH" \
               --title "$pr_title" \