add pip-audit step to official build

Author: Victoria Hall

eng/templates/build.yml

@@ -23,6 +23,9 @@ jobs:
         displayName: 'Check python version'
       - bash: |
           python -m pip install -U pip
-          pip install twine wheel
+          pip install twine wheel pip-audit
           python setup.py sdist bdist_wheel
         displayName: 'Build Python SDK'
+      - bash: |
+          pip-audit
+        displayName: 'Run vulnerability scan'