Specifying nuget config path.

Author: mijpeterson

.github/workflows/pr-azure-pipelines.yml

@@ -73,6 +73,7 @@ extends:
               feedsToUse: select
               vstsFeed: $(VSTS_FEED_ID)
               includeNuGetOrg: false
+              nugetConfigPath: 'nuget.config'
           # 1ES PT requires explicit build task for Roslyn analysis. Auto-injected Roslyn task will use build logs from this build.
           - task: DotNetCoreCLI@2
             displayName: Build projects