NettyReactiveWebServerFactoryTests.portInUseExceptionIsThrownWhenPortIsAlreadyInUse
started failing on CI following this change in reactor netty:
e6634c27f6
Instead of a `BindException`, a `NativeIoException` is thrown. Since that Exception
is for internal use only, we throw a generic `WebServerException`
instead of the `PortInUseException`.