CI: Use Python 3.8 on all OSes

Co-authored-by: Amin Yahyaabadi <[email protected]>

Author: DeeDeeG

script/vsts/platforms/templates/preparation.yml

@@ -28,6 +28,10 @@ steps:
   - script: npm install --global [email protected]
     displayName: Update npm
 
+  - task: UsePythonVersion@0
+    inputs:
+      versionSpec: '3.8'
+
   # Use Azure Syntax to set env variables for all shells and steps
   - pwsh: |
       if ($env:AGENT_OS -eq "Windows_NT") {