Move dotnet watch to a seperate test group (#6730)

Author: pakrym

src/Tools/dotnet-watch/test/dotnet-watch.Tests.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>netcoreapp2.1</TargetFramework>
     <AssemblyName>Microsoft.DotNet.Watcher.Tools.Tests</AssemblyName>
     <DefaultItemExcludes>$(DefaultItemExcludes);TestProjects\**\*</DefaultItemExcludes>
+    <TestGroupName>DotNetWatcherToolsTests</TestGroupName>
   </PropertyGroup>
 
   <ItemGroup>