Consistent @Bean method return type for equivalence with XML example

Closes gh-29970

src/docs/asciidoc/core/core-beans.adoc

@@ -7596,7 +7596,7 @@ The simplest possible `@Configuration` class reads as follows:
 	public class AppConfig {
 
 		@Bean
-		public MyService myService() {
+		public MyServiceImpl myService() {
 			return new MyServiceImpl();
 		}
 	}
@@ -7608,7 +7608,7 @@ The simplest possible `@Configuration` class reads as follows:
 	class AppConfig {
 
 		@Bean
-		fun myService(): MyService {
+		fun myService(): MyServiceImpl {
 			return MyServiceImpl()
 		}
 	}