Fix race condition in SnapshotMetricsIT.testSnapshotAPMMetrics (#132686)

Moves the new code that updates the snapshot completed metrics
to before the snapshot listeners are completed.  This mirrors
how the listener is completed after the snapshot started metric
is updated.

Resolves: #132672

Author: JeremyDahlgren

muted-tests.yml

@@ -515,9 +515,6 @@ tests:
 - class: org.elasticsearch.xpack.sql.action.SqlSearchPageTimeoutIT
   method: testSearchContextIsCleanedUpAfterPageTimeoutForAggregationQueries
   issue: https://github.com/elastic/elasticsearch/issues/132619
-- class: org.elasticsearch.repositories.SnapshotMetricsIT
-  method: testSnapshotAPMMetrics
-  issue: https://github.com/elastic/elasticsearch/issues/132672
 - class: org.elasticsearch.xpack.ml.integration.TextEmbeddingQueryIT
   method: testHybridSearch
   issue: https://github.com/elastic/elasticsearch/issues/132703

server/src/main/java/org/elasticsearch/snapshots/SnapshotsService.java

@@ -1232,7 +1232,6 @@ protected void doRun() {
                         () -> snapshotListeners.addListener(new ActionListener<>() {
                             @Override
                             public void onResponse(List<ActionListener<SnapshotInfo>> actionListeners) {
-                                SnapshotsServiceUtils.completeListenersIgnoringException(actionListeners, snapshotInfo);
                                 final Map<String, Object> attributesWithState = Maps.copyMapWithAddedEntry(
                                     SnapshotMetrics.createAttributesMap(snapshot.getProjectId(), repo.getMetadata()),
                                     "state",
@@ -1241,6 +1240,7 @@ public void onResponse(List<ActionListener<SnapshotInfo>> actionListeners) {
                                 snapshotMetrics.snapshotsCompletedCounter().incrementBy(1, attributesWithState);
                                 snapshotMetrics.snapshotsDurationHistogram()
                                     .record((snapshotInfo.endTime() - snapshotInfo.startTime()) / 1_000.0, attributesWithState);
+                                SnapshotsServiceUtils.completeListenersIgnoringException(actionListeners, snapshotInfo);
                                 logger.info("snapshot [{}] completed with state [{}]", snapshot, snapshotInfo.state());
                             }