fix: samples/client/petstore/spring-cloud-feign-without-url/pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-ORGSPRINGFRAMEWORK-12817817

Author: snyk-bot

samples/client/petstore/spring-cloud-feign-without-url/pom.xml

@@ -55,7 +55,7 @@
         <dependency>
             <groupId>org.springframework.security</groupId>
             <artifactId>spring-security-oauth2-client</artifactId>
-            <version>5.7.8</version>
+            <version>6.4.11</version>
         </dependency>
         <dependency>
             <groupId>com.fasterxml.jackson.datatype</groupId>