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
...

Signed-off-by: dependabot[bot] <support@github.com>

pom.xml

@@ -974,7 +974,7 @@
             <dependency>
                 <groupId>com.thoughtworks.xstream</groupId>
                 <artifactId>xstream</artifactId>
-                <version>1.4.20</version>
+                <version>1.4.21</version>
                 <exclusions>
                     <exclusion>
                         <groupId>io.github.x-stream</groupId>