[AzurePipeline] Fix vstest step failed by libyang missing. (sonic-net#12240)

Why I did it
Fix PR merge failed because 'vstest' step does not install libyang.

How I did it
Install libyang in azure pipeline.

How to verify it
Pass vstest step.

Author: liuh-80

azure-pipelines.yml

@@ -113,6 +113,8 @@ stages:
 
     - script: |
         set -x
+        sudo apt-get update
+        sudo apt-get install libyang0.16 -y
         sudo dpkg -i --force-confask,confnew ../libswsscommon_1.0.0_amd64.deb
         sudo dpkg -i ../python3-swsscommon_1.0.0_amd64.deb
         sudo docker load -i ../target/docker-sonic-vs.gz