adding a pip freeze to ensure we fully understand what our environment has (#12173)

Author: scbedd

eng/pipelines/templates/steps/build-test.yml

@@ -29,6 +29,7 @@ steps:
       python -m pip install pip==20.1
       pip install -r eng/ci_tools.txt
       pip --version
+      pip freeze
     displayName: 'Prep Environment'
 
   - ${{ parameters.BeforeTestSteps }}