Update struts2.version

Author: renovate[bot]

pom.xml

@@ -84,7 +84,7 @@
     <openrtf.version>1.2.1</openrtf.version>
     <owasp-java-html-sanitizer.version>20220608.1</owasp-java-html-sanitizer.version>
     <servlet-api.version>3.0.1</servlet-api.version>
-    <struts2.version>2.5.33</struts2.version>
+    <struts2.version>6.4.0</struts2.version>
     <validation-api.version>2.0.1.Final</validation-api.version>
     <hibernate-validator.version>6.2.5.Final</hibernate-validator.version>
     <jakarta.el.version>3.0.4</jakarta.el.version>