fix pipeline linux job demands

Author: afifi-ins

azure-pipelines-arcade-PR.yml

@@ -149,7 +149,7 @@ stages:
           container: ubuntu_2004_20211215
           pool:
             name:  NetCore-Public
-            demands: ImageOverride -equals build.Ubuntu.1804.Amd64.Open
+            demands: ImageOverride -equals build.Ubuntu.2004.Amd64.Open
           variables:
           - _TestArgs: /p:ServiceUri=$(_serviceUri) /p:Root_Certificate_Installed=true /p:Client_Certificate_Installed=true /p:SSL_Available=true
           - _serviceUri: