Fix importance check for target-skipped messages
https://github.com/dotnet/msbuild/pull/12226 introduced a bug: MessageImportance.Low is (numerically) the highest value, so nothing is ever greater than it is. This caused the problems observed in https://github.com/microsoft/testfx/pull/6426 (thanks @Youssef1313 for diagnosing this!).
Reverse the comparison and extract a method to avoid this confusion in the future.
Any update here please @rainersigwald ?
Ping @rainersigwald
Unfortunately it looks like this is not going to be fixed in 10.0.1xx. VS would consider it a regression so we need a deeper solution.
@rainersigwald @baronfel any news about this bug?