Use extra-index-url for aarch64 builds (#1503)

Author: atalman

.github/workflows/validate-aarch64-linux-binaries.yml

@@ -69,6 +69,8 @@ jobs:
         source ./aarch64_linux/aarch64_ci_setup.sh
         echo "/opt/conda/bin" >> $GITHUB_PATH
 
+        MATRIX_INSTALLATION=${MATRIX_INSTALLATION/"index-url"/"extra-index-url"}
+
         export ENV_NAME="conda-env-${{ github.run_id }}"
         export TARGET_OS="linux-aarch64"
         export TORCH_ONLY=${{ inputs.torchonly }}