fix: samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-ORGSPRINGFRAMEWORKSECURITY-9486467

Author: snyk-bot

samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/pom.xml

@@ -54,7 +54,7 @@
         <dependency>
             <groupId>org.springframework.security</groupId>
             <artifactId>spring-security-oauth2-client</artifactId>
-            <version>5.7.8</version>
+            <version>6.3.8</version>
         </dependency>
         <dependency>
             <groupId>com.fasterxml.jackson.datatype</groupId>