Name the unused Mockito answer parameter for Java 21 compatibility

ReplicationQueueTest used an unnamed variable (`_`) as the thenAnswer
lambda parameter. Unnamed variables are a standard feature only in
Java 22+; under a Java 21 language level they are a disabled preview
feature and fail to compile. Give the parameter a name so the test
builds on both Java 21 and Java 25.

Change-Id: Ib121547711a022a1ec1304289b905cb6c5f54428

src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationQueueTest.java

diff --git a/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationQueueTest.java b/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationQueueTest.java
index adb16c9..3a10570 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationQueueTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/replication/ReplicationQueueTest.java
@@ -76,7 +76,7 @@
     when(destinations.getDestinations(any(), any(), any())).thenReturn(List.of(destination));
 
     ReplicationTasksStorage tasksStorage = mock(ReplicationTasksStorage.class);
-    when(tasksStorage.streamWaiting()).thenAnswer(_ -> List.copyOf(waitingTasks).stream());
+    when(tasksStorage.streamWaiting()).thenAnswer(invocation -> List.copyOf(waitingTasks).stream());
 
     defaultQueue = new ScheduledThreadPoolExecutor(1);
     workQueue = mock(WorkQueue.class);