Only upload docs for CI build and not pull requests (GH-6945)

diff --git a/.vsts/docs.yml b/.vsts/docs.yml
index efa1e87..62f6123 100644
--- a/.vsts/docs.yml
+++ b/.vsts/docs.yml
@@ -37,6 +37,7 @@
 
 - task: PublishBuildArtifacts@1
   displayName: 'Publish build'
+  condition: and(succeeded(), ne(variables['Build.Reason'], 'PullRequest'))
   inputs:
     PathToPublish: '$(build.sourcesDirectory)/Doc/build'
     ArtifactName: build