[Blazor] Concurrency build issues on CI

[javiercn]

Seems our build is doing some things concurrently which are causing issues. See the errors reported in the link below.

https://dev.azure.com/dnceng/public/_build/results?buildId=1414586&view=results

[javiercn]

Another example of this issue

https://dev.azure.com/dnceng/public/_build/results?buildId=1414350&view=logs&j=f43b187f-6c15-531c-a59b-e4fba4e9ed20&t=98a09275-a4dd-593e-c21a-1f8bea3be5b1

I suspect this is the case based on the fact that the issue is on BasicTestApp

[mkArtakMSFT]

Closing as this seems to have been addressed already.