[Nuget] Update signing (#12016)

azure-pipelines.yml

@@ -26,6 +26,7 @@ resources:
       type: github
       name: xamarin/yaml-templates
       endpoint: xamarin
+      ref: refs/heads/main # still defaults to master even though main is the main branch
 
 trigger:
   branches:

build/steps/build-sign.yml

@@ -19,6 +19,7 @@ steps:
       jenkinsEndpoint: Xamarin Code Signing Jenkins
       jenkinsJob: sign-from-vsts
       artifactHost: 'https://dl.internalx.com/vsts-devdiv'
+      CodeSignOverride: true
 
   - task: PublishBuildArtifacts@1
     displayName: 'Publish Artifact: nuget signed'