Adapt MyBeanRegistrar Kotlin code sample

This commit adapts the MyBeanRegistrar Kotlin code sample to use a
lambda supplier instead of a callable reference since this capability
has been removed.

See gh-35549
Closes gh-35694

framework-docs/src/main/kotlin/org/springframework/docs/core/beans/java/beansjavaprogrammaticregistration/MyBeanRegistrar.kt

@@ -33,7 +33,9 @@ class MyBeanRegistrar : BeanRegistrarDsl({
 		registerBean { Baz("Hello World!") }
 	}
 	registerBean<MyRepository>()
-	registerBean(::myRouter)
+	registerBean {
+		myRouter(bean<MyRepository>()) // Also possible with just myRouter(bean())
+	}
 })
 
 fun myRouter(myRepository: MyRepository) = router {