Update onebranch-windows-build-stage.yml

Author: wenbingl

.pipelines/templates/onebranch-windows-build-stage.yml

@@ -48,6 +48,7 @@ stages:
         @echo ##vso[task.setvariable variable=vsmsbuild]%vsmsbuild%
       displayName: 'locate vsdevcmd via vswhere'
 
+    - task: UsePythonVersion@0
     - script: |
         call $(vsdevcmd) -arch=amd64
         set PYTHONPATH=