Update DiffRunner.cs

Author: SimonCropp

src/DiffEngine/DiffRunner.cs

@@ -244,7 +244,8 @@ static int LaunchProcess(ResolvedTool tool, string arguments)
             // Given the full exe path is known we dont need UseShellExecute https://stackoverflow.com/a/5255335
             // however UseShellExecute allows the test running to not block when the difftool is launched
             // https://github.com/VerifyTests/Verify/issues/1229
-            UseShellExecute = true
+            UseShellExecute = true,
+            CreateNoWindow = tool.CreateNoWindow
         };
         try
         {