Fix upstream sync checkout (#130)

* Checkout main before trying to switch to it

* Fix the checkout command

Author: charleshofer

.github/workflows/rocm-nightly-upstream-sync.yml

@@ -29,7 +29,8 @@ jobs:
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683  # v4.2.2
       - name: Create branch
         run: |
-          git checkout -b $SYNC_BRANCH_NAME main
+          git checkout origin/main 
+          git checkout -b $SYNC_BRANCH_NAME
           git push origin HEAD
   open-sync-pr:
     needs: create-sync-branch