ZipkinConfigurations.SenderConfiguration uses @ConditionalOnClass on a @Bean method

`org.springframework.boot.actuate.autoconfigure.tracing.zipkin.ZipkinConfigurations.SenderConfiguration#urlConnectionSender` has a `@ConditionalOnClass(URLConnectionSender.class)` on it. This annotation is not supported at method level. Make sure that the methods returns the most concrete type possible.