Re-enable venv for testing (#36465)

* use a venv for test steps

Author: scbedd

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

@@ -31,6 +31,8 @@ steps:
     parameters:
       versionSpec: '${{ parameters.PythonVersion }}'
 
+  - template: /eng/pipelines/templates/steps/use-venv.yml
+
   - template: set-dev-build.yml
     parameters:
       ServiceDirectory: ${{ parameters.ServiceDirectory }}