deps(webgoat): bump com.thoughtworks.xstream:xstream in /WebGoat

Bumps [com.thoughtworks.xstream:xstream](https://github.com/x-stream/xstream) from 1.4.5 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-version: 1.4.21
  dependency-type: direct:production
...

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

Author: dependabot[bot]

WebGoat/pom.xml

@@ -105,7 +105,7 @@
     <webwolf.port>9090</webwolf.port>
     <wiremock.version>3.13.1</wiremock.version>
     <xml-resolver.version>1.2</xml-resolver.version>
-    <xstream.version>1.4.5</xstream.version>
+    <xstream.version>1.4.21</xstream.version>
     <!-- do not update necessary for lesson -->
     <zxcvbn.version>1.9.0</zxcvbn.version>
   </properties>