fix: samples/openapi3/client/petstore/spring-cloud-3/pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-ORGSPRINGFRAMEWORK-12008931

Author: snyk-bot

samples/openapi3/client/petstore/spring-cloud-3/pom.xml

@@ -10,7 +10,7 @@
         <maven.compiler.source>${java.version}</maven.compiler.source>
         <maven.compiler.target>${java.version}</maven.compiler.target>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <springdoc.version>2.2.0</springdoc.version>
+        <springdoc.version>2.8.11</springdoc.version>
     </properties>
     <parent>
         <groupId>org.springframework.boot</groupId>