fix: samples/client/petstore/java/google-api-client/pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-COMGOOGLEGUAVA-5710356

Author: snyk-bot

samples/client/petstore/java/google-api-client/pom.xml

@@ -259,7 +259,7 @@
     </dependencies>
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <google-api-client-version>2.2.0</google-api-client-version>
+        <google-api-client-version>2.6.0</google-api-client-version>
         <jersey-common-version>2.40</jersey-common-version>
         <jackson-version>2.17.1</jackson-version>
         <jackson-databind-version>2.17.1</jackson-databind-version>