Update Checkout Lean Same Branch ref to actual branch name

Use `github.head_ref || github.ref_name` instead of `github.ref` so the
Lean checkout resolves to the actual branch name across push and pull
request events.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: jhonabreul

.github/workflows/gh-actions.yml

@@ -29,7 +29,7 @@ jobs:
         uses: actions/checkout@v2
         continue-on-error: true
         with:
-          ref: ${{ github.ref }}
+          ref: ${{ github.head_ref || github.ref_name }}
           repository: QuantConnect/Lean
           path: Lean