Mark node seen task as successful

The task for updating cluster state with nodes seen by shutdown was
previously switched to use batched tasks. However, the task is never
marked as complete, which leads to the tasks piling up. This commit
marks the task as complete and re-enables a test that appears to succeed
now.

closes elastic#76689

x-pack/plugin/shutdown/src/internalClusterTest/java/org/elasticsearch/xpack/shutdown/NodeShutdownShardsIT.java

@@ -70,7 +70,6 @@ public void testShardStatusStaysCompleteAfterNodeLeaves() throws Exception {
      * Similar to the previous test, but ensures that the status stays at `COMPLETE` when the node is offline when the shutdown is
      * registered. This may happen if {@link NodeSeenService} isn't working as expected.
      */
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/76689")
     public void testShardStatusStaysCompleteAfterNodeLeavesIfRegisteredWhileNodeOffline() throws Exception {
         assumeTrue("must be on a snapshot build of ES to run in order for the feature flag to be set", Build.current().isSnapshot());
         final String nodeToRestartName = internalCluster().startNode();
@@ -88,11 +87,12 @@ public Settings onNodeStopped(String nodeName) throws Exception {
         });
 
         internalCluster().stopNode(nodeToRestartName);
+        putNodeShutdown(nodeToRestartId, SingleNodeShutdownMetadata.Type.REMOVE, null);
 
         NodesInfoResponse nodes = clusterAdmin().prepareNodesInfo().clear().get();
         assertThat(nodes.getNodes().size(), equalTo(1));
 
-        assertNodeShutdownStatus(nodeToRestartId, COMPLETE);
+        assertBusy(() -> { assertNodeShutdownStatus(nodeToRestartId, COMPLETE); });
     }
 
     /**

x-pack/plugin/shutdown/src/main/java/org/elasticsearch/xpack/shutdown/NodeSeenService.java

@@ -101,6 +101,7 @@ public ClusterState execute(BatchExecutionContext<SetSeenNodesShutdownTask> batc
             var nodesNotPreviouslySeen = new HashSet<>();
             for (final var taskContext : batchExecutionContext.taskContexts()) {
                 nodesNotPreviouslySeen.addAll(taskContext.getTask().nodesNotPreviouslySeen());
+                taskContext.success(() -> {});
             }
 
             var nodes = initialState.nodes();