Bump spring-framework-bom in /examples/restful-ws-spring-boot (#423)

Bumps [spring-framework-bom](https://github.com/spring-projects/spring-framework) from 5.2.8.RELEASE to 5.2.9.RELEASE.
- [Release notes](https://github.com/spring-projects/spring-framework/releases)
- [Commits](spring-projects/spring-framework@v5.2.8.RELEASE...v5.2.9.RELEASE)

---
updated-dependencies:
- dependency-name: org.springframework:spring-framework-bom
  dependency-type: direct:production
...

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examples/restful-ws-spring-boot/pom.xml

@@ -13,7 +13,7 @@
 
     <properties>
         <spring-boot.version>2.3.2.RELEASE</spring-boot.version>
-        <spring.version>5.2.8.RELEASE</spring.version>
+        <spring.version>5.2.9.RELEASE</spring.version>
     </properties>
 
     <dependencyManagement>