Fix --else-if-branch on main

https://github.com/candy-lang/candy/actions/runs/8102406067/job/22144811058

.github/workflows/compiler.yaml

@@ -207,7 +207,7 @@ jobs:
             --project candy \
             --token ${{ secrets.BENCHER_TOKEN }} \
             --if-branch ${{ github.head_ref || github.ref_name }} \
-            --else-if-branch ${{ github.base_ref }} \
+            ${{ github.base_ref && format('--else-if-branch {0}', github.base_ref) || '' }} \
             --else-if-branch main \
             --hash ${{ github.event_name == 'pull_request' && github.event.pull_request.head.sha || github.sha }} \
             --testbed github-actions-ubuntu-22-04 \