Bump com.thoughtworks.xstream:xstream from 1.4.20 to 1.4.21

Bumps [com.thoughtworks.xstream:xstream](https://github.com/x-stream/xstream) from 1.4.20 to 1.4.21.
- [Release notes](https://github.com/x-stream/xstream/releases)
- [Commits](https://github.com/x-stream/xstream/commits)

---
updated-dependencies:
- dependency-name: com.thoughtworks.xstream:xstream
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

pom.xml

@@ -107,7 +107,7 @@
     <roaster.version>2.29.0.Final</roaster.version>
     <takari-smart-builder.version>1.0.2</takari-smart-builder.version>
     <testcontainers.version>1.20.3</testcontainers.version>
-    <xstream.version>1.4.20</xstream.version>
+    <xstream.version>1.4.21</xstream.version>
   </properties>
 
   <dependencyManagement>