Updated the perf file with Python version 3.8

vsts_ci/continuous-perf.yml

@@ -5,7 +5,7 @@ steps:
 - task: UsePythonVersion@0
   displayName: "Use Python 3.8"
   inputs:
-    versionSpec: 3.8.7
+    versionSpec: 3.8
 
 - task: AzureCLI@2
   displayName: 'Run All Performance Tests'