[ci] Disable vstest job in Test stage. (#21354)

Disable vstest job because sonictest agent pool is failing.
To unblock PRs.

Author: liushilongbuaa

azure-pipelines.yml

@@ -109,6 +109,7 @@ stages:
   - job:
     pool: sonictest
     displayName: "vstest"
+    condition: false # agent pool don't work. disable this job to unblock PRs.
     timeoutInMinutes: 60
     steps:
     - template: .azure-pipelines/cleanup.yml