add some code to discover what versions of Python are available on the build agent

.azure/ci-windows-job.yml

@@ -49,6 +49,8 @@ jobs:
   - bash: |
       which python
       python -c "import sys; print(sys.version); print(sys.prefix)"
+      # check what Pythons are available
+      ls -al /c/hostedtoolcache/windows/Python
     displayName: 'Check Python'
 
   - bash: |