Fix Checkstyle violation for import order in the HandlerAdapter

Author: artembilan

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/listener/adapter/HandlerAdapter.java

@@ -20,8 +20,8 @@
 import java.lang.reflect.Type;
 import java.util.concurrent.CompletableFuture;
 
-import org.springframework.lang.Nullable;
 import org.springframework.core.KotlinDetector;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.handler.invocation.InvocableHandlerMethod;