Exclude *.approved.cs-files from license header check.

Rx.NET/Source/tests/Tests.System.Reactive/Tests/LicenseHeaderTest.cs

@@ -53,6 +53,7 @@ namespace Tests.System.Reactive.Tests
                     || file.Contains("AssemblyInfo.cs")
                     || file.Contains(".Designer.cs")
                     || file.Contains(".Generated.cs")
+                    || file.Contains(".approved.cs")
                     || file.Contains("Uwp.DeviceRunner")
                 )
                 {