fix: samples/client/petstore/java/retrofit2-play26/pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-COMSQUAREUPOKHTTP3-13961111

Author: snyk-bot

samples/client/petstore/java/retrofit2-play26/pom.xml

@@ -307,7 +307,7 @@
         <jackson-databind-nullable-version>0.2.7</jackson-databind-nullable-version>
         <javax.ws.rs-api-version>2.1.1</javax.ws.rs-api-version>
         <play-version>2.6.7</play-version>
-        <retrofit-version>2.11.0</retrofit-version>
+        <retrofit-version>3.0.0</retrofit-version>
         <jakarta-annotation-version>2.1.1</jakarta-annotation-version>
         <beanvalidation-version>3.0.2</beanvalidation-version>
         <oltu-version>1.0.1</oltu-version>