[Infra] Flaky CSharpIntegration Windows

https://dev.azure.com/dnceng-public/public/_build/results?buildId=1117210&view=ms.vss-test-web.build-test-results-tab

Based on the symptoms, it looks like something is going wrong with the project loading - hover is fully qualifying namespaces (e.g. System.Exception, vs Exception - it should be Exception due to usings), completion is reporting generic items, diagnostics are missing, classification says everything is a 'variable'. I am guessing something related to msbuildworkspace stuff since devkit tests are not having the same issue.