Bump com.thoughtworks.xstream:xstream from 1.4.19 to 1.4.21

Bumps [com.thoughtworks.xstream:xstream](https://github.com/x-stream/xstream) from 1.4.19 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] <support@github.com>

redis-persistence/build.gradle

@@ -18,7 +18,7 @@ dependencies {
 
     implementation "redis.clients:jedis:${revJedis}"
     implementation "com.netflix.dyno-queues:dyno-queues-redis:${revDynoQueues}"
-    implementation('com.thoughtworks.xstream:xstream:1.4.19')
+    implementation('com.thoughtworks.xstream:xstream:1.4.21')
 
     //In memory
     implementation "org.rarefiedredis.redis:redis-java:${revRarefiedRedis}"