chore(deps): update dependency com.thoughtworks.xstream:xstream to v1.4.21 [security]

Author: renovate[bot]

pom.xml

@@ -551,7 +551,7 @@
     <dependency>
       <groupId>com.thoughtworks.xstream</groupId>
       <artifactId>xstream</artifactId>
-      <version>1.4.20</version>
+      <version>1.4.21</version>
       <optional>true</optional>
     </dependency>
     <dependency>