fix: samples/server/petstore/spring-mvc-j8-async/pom.xml to reduce vu…

…lnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-ORGSPRINGFRAMEWORK-7945490

samples/server/petstore/spring-mvc-j8-async/pom.xml

@@ -173,7 +173,7 @@
         <jackson-version>2.9.9</jackson-version>
         <jackson-threetenbp-version>2.8.4</jackson-threetenbp-version>
         <beanvalidation-version>1.1.0.Final</beanvalidation-version>
-        <spring-version>4.3.20.RELEASE</spring-version>
+        <spring-version>6.1.13</spring-version>
         <jackson-databind-nullable-version>0.2.1</jackson-databind-nullable-version>
         <jackson-databind-version>2.9.8</jackson-databind-version>
     </properties>