fix: samples/client/echo_api/java/restclient/pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-COMFASTERXMLJACKSONCORE-15365924

Author: snyk-bot

samples/client/echo_api/java/restclient/pom.xml

@@ -275,8 +275,8 @@
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <spring-web-version>6.1.21</spring-web-version>
-        <jackson-version>2.19.2</jackson-version>
-        <jackson-databind-version>2.19.2</jackson-databind-version>
+        <jackson-version>2.21.1</jackson-version>
+        <jackson-databind-version>2.21.1</jackson-databind-version>
         <jackson-databind-nullable-version>0.2.7</jackson-databind-nullable-version>
         <jakarta-annotation-version>2.1.1</jakarta-annotation-version>
         <beanvalidation-version>3.0.2</beanvalidation-version>