[CI] Use isPR parameter instead of the build reason on publishing nugets. (#15283)

tools/devops/automation/templates/sign-and-notarized/dotnet-signing.yml

@@ -96,6 +96,8 @@ steps:
   workingDirectory: $(Build.ArtifactStagingDirectory)
 
 - template: publish-nugets.yml
+  parameters:
+    isPR: ${{ parameters.isPR }}
 
 # always upload no matter what, since if we are not signing we need the artifact in the pipeline
 - task: PublishPipelineArtifact@1

tools/devops/automation/templates/sign-and-notarized/publish-nugets.yml

@@ -1,9 +1,13 @@
 # all steps that are required to publish the nugets
 
+parameters:
+- name: isPR
+  type: boolean
+
 steps:
 
 # do not publish on pull requets
-- ${{ if ne(variables['Build.Reason'], 'PullRequest') }}:
+- ${{ if not(parameters.isPR) }}:
   - task: NuGetCommand@2
     displayName: 'Publish Nugets to dotnet-eng'
     inputs: