Polish LDAP serialization

Closes gh-9263

core/src/main/java/org/springframework/security/jackson2/SecurityJackson2Modules.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015-2020 the original author or authors.
+ * Copyright 2015-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -209,6 +209,7 @@ public final class SecurityJackson2Modules {
 			names.add("java.util.HashMap");
 			names.add("java.util.LinkedHashMap");
 			names.add("org.springframework.security.core.context.SecurityContextImpl");
+			names.add("java.util.Arrays$ArrayList");
 			ALLOWLIST_CLASS_NAMES = Collections.unmodifiableSet(names);
 		}