Skipped test: dotnet-watch crash on OSX

[pranavkm]

Noticed this in a few builds where dotnet-watch test run appear to be crashing in the OSX leg. Skipping these until we can root cause the failure:

https://dev.azure.com/dnceng/public/_build/results?buildId=820179&view=ms.vss-test-web.build-test-results-tab&runId=26101576&paneView=debug&resultId=122334