Fix property placeholder references in @value example

See gh-31941

Author: vilmos

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

@@ -1236,8 +1236,8 @@ The following table summarizes the features that are supported by `@Configuratio
 If you do want to use `@Value`, we recommend that you refer to property names using their canonical form (kebab-case using only lowercase letters).
 This will allow Spring Boot to use the same logic as it does when <<features#features.external-config.typesafe-configuration-properties.relaxed-binding, relaxed binding>> `@ConfigurationProperties`.
 
-For example, `@Value("{demo.item-price}")` will pick up `demo.item-price` and `demo.itemPrice` forms from the `application.properties` file, as well as `DEMO_ITEMPRICE` from the system environment.
-If you used `@Value("{demo.itemPrice}")` instead, `demo.item-price` and `DEMO_ITEMPRICE` would not be considered.
+For example, `@Value("${demo.item-price}")` will pick up `demo.item-price` and `demo.itemPrice` forms from the `application.properties` file, as well as `DEMO_ITEMPRICE` from the system environment.
+If you used `@Value("${demo.itemPrice}")` instead, `demo.item-price` and `DEMO_ITEMPRICE` would not be considered.
 ====
 
 If you define a set of configuration keys for your own components, we recommend you group them in a POJO annotated with `@ConfigurationProperties`.