Merge pull request #28670 from weixsun

* pr/28670:
  Polish "Fix yaml sample format in reference doc"
  Fix yaml sample format in reference doc

Closes gh-28670

Author: snicoll

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/external-config.adoc

@@ -470,10 +470,16 @@ For example, the following file has two logical documents:
 
 [source,yaml,indent=0,subs="verbatim"]
 ----
-	spring.application.name: MyApp
+	spring:
+	  application:
+	    name: MyApp
 	---
-	spring.config.activate.on-cloud-platform: kubernetes
-	spring.application.name: MyCloudApp
+	spring:
+	  application:
+	    name: MyCloudApp
+	  config:
+	    activate:
+	      on-cloud-platform: kubernetes
 ----
 
 For `application.properties` files a special `#---` comment is used to mark the document splits:
@@ -482,8 +488,8 @@ For `application.properties` files a special `#---` comment is used to mark the
 ----
 	spring.application.name=MyApp
 	#---
-	spring.config.activate.on-cloud-platform=kubernetes
 	spring.application.name=MyCloudApp
+	spring.config.activate.on-cloud-platform=kubernetes
 ----
 
 NOTE: Property file separators must not have any leading whitespace and must have exactly three hyphen characters.