chore: Update RELEASE.md (#10767)

Signed-off-by: Chen Sun <chensun@users.noreply.github.com>

RELEASE.md

@@ -237,15 +237,15 @@ and then "Retry", because after waiting for previous step, artifacts are now rea
     cd backend/api/v2beta1/python_http_client
     rm -r dist
     python3 setup.py --quiet sdist
-    python3 -m twine upload --username kubeflow-pipelines dist/*
+    python3 -m twine upload dist/*
     ```
 
 1. Release `kfp` python packages to PyPI. (Note: Please skip this step for backend release, this step will be handled by SDK release.)
 
     ```bash
     pip3 install twine --user
     gsutil cp gs://ml-pipeline/release/$VERSION/kfp.tar.gz kfp-$VERSION.tar.gz
-    python3 -m twine upload --username kubeflow-pipelines kfp-$VERSION.tar.gz
+    python3 -m twine upload kfp-$VERSION.tar.gz
     ```
 
     !!! The file name must contain the version. See <https://github.com/kubeflow/pipelines/issues/1292>