Bump spring-boot-starter-data-mongodb in /plugins/maven/example-client (#490)

Bumps [spring-boot-starter-data-mongodb](https://github.com/spring-projects/spring-boot) from 2.4.1 to 2.4.2.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.4.1...v2.4.2)

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plugins/maven/example-client/pom.xml

@@ -124,7 +124,7 @@
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-data-mongodb</artifactId>
-            <version>2.4.1</version>
+            <version>2.4.2</version>
         </dependency>
 
         <dependency>