[Nova] Fix Refs in Build Workflow to use Default GitHub Ref (#6863)

Author: osalpekar

.github/workflows/build-conda-linux.yml

@@ -32,6 +32,7 @@ jobs:
     with:
       conda-package-directory: ${{ matrix.conda-package-directory }}
       repository: ${{ matrix.repository }}
+      ref: ""
       test-infra-repository: pytorch/test-infra
       test-infra-ref: main
       build-matrix: ${{ needs.generate-matrix.outputs.matrix }}