fix: benchmark/pom.xml to reduce vulnerabilities (#1502)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-IONETTY-1584063
- https://snyk.io/vuln/SNYK-JAVA-IONETTY-1584064

Co-authored-by: Marvin Froeder <velo@users.noreply.github.com>

benchmark/pom.xml

@@ -30,7 +30,7 @@
     <jmh.version>1.33</jmh.version>
     <rx.netty.version>0.5.3</rx.netty.version>
     <rx.java.version>1.3.8</rx.java.version>
-    <netty.version>4.1.67.Final</netty.version>
+    <netty.version>4.1.68.Final</netty.version>
 
     <main.basedir>${project.basedir}/..</main.basedir>
   </properties>