Disabling Mono leg

Latest Mono nightly builds appear to have broken serialization during
remoting across AppDomain instances. That is pretty fundamental to how
we test. Temporarily disabling the Mono leg until this can be fixed.

Tracking Mono Issue: https://github.com/mono/mono/issues/16373

azure-pipelines.yml

@@ -183,10 +183,11 @@ jobs:
         _args: --testCoreClr --docker
         _name: CoreClr
         _configuration: Debug
-      mono:
-        _args: --testMono --docker
-        _name: Mono
-        _configuration: Debug
+# Disabling Mono while https://github.com/mono/mono/issues/16373 is worked out
+#      mono:
+#        _args: --testMono --docker
+#        _name: Mono
+#        _configuration: Debug
   timeoutInMinutes: 90
   steps:
     - script: ./eng/cibuild.sh --configuration $(_configuration) --prepareMachine $(_args)