Updated API Diff Files are not being published

[ellahathaway]

The updated API diff file is not being published as an artifact in the SDK diff test pipeline runs:

This makes fixing #5378 difficult.

[MichaelSimons]

I think this was fixed in dotnet/dotnet#2829. Looks like it wasn't backported. @NikolaMilosavljevic can you take care of this? Not sure if the baseline change that was included in the PR can/should be backported as well.