Call NuGetAuthenticate after SetupNuGetSources (#55960)

The new version of the powershell script will not place the creds in the nuget.config file, instead it will use standard environment variables. Update the YAML file to use NuGetAuthenticate to avoid a build break that may happen if the credential provider is not available.

Author: mmitche

.azure/pipelines/jobs/default-build.yml

@@ -436,6 +436,9 @@ jobs:
           env:
             Token: $(dn-bot-dnceng-artifact-feeds-rw)
 
+      # Call the NugetAuthenticate task to add creds for added feeds.
+      - task: NuGetAuthenticate@1
+
       # Add COMPlus_* environment variables to build steps.
       - ${{ if ne(parameters.steps, '')}}:
         - ${{ each step in parameters.steps }}: