Fix name of branch for action-send-mail

.github/workflows/smoke-test.yml

@@ -40,7 +40,7 @@ jobs:
         python -m pytest
     - name: Send status to author's email      
       if: ${{ failure() }} && github.event_name != 'workflow_dispatch' }} # Only email if the workflow failed and was not manually started. Customize this as necessary.
-      uses: dawidd6/action-send-mail@main
+      uses: dawidd6/action-send-mail@master
       with:
         # Required mail server address if not connection_url:
         server_address: smtp.gmail.com