Avoid null threadContext in ResultDeduplicator

In elastic#84038 we added a dependency on having a valid `threadContext` in a
repository, but some tests use mocking and may end up with a `null`
here. This seems not to be a problem in recent branches but causes
failures in 8.0. With this commit we ensure that we always have a valid
`threadContext` to avoid any problems.

server/src/main/java/org/elasticsearch/action/ResultDeduplicator.java

@@ -28,6 +28,7 @@ public final class ResultDeduplicator<T, R> {
     private final ConcurrentMap<T, CompositeListener> requests = ConcurrentCollections.newConcurrentMap();
 
     public ResultDeduplicator(ThreadContext threadContext) {
+        assert threadContext != null;
         this.threadContext = threadContext;
     }
 

server/src/test/java/org/elasticsearch/repositories/RepositoriesServiceTests.java

@@ -31,6 +31,7 @@
 import org.elasticsearch.common.component.LifecycleListener;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.util.MockBigArrays;
+import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.index.snapshots.IndexShardSnapshotStatus;
 import org.elasticsearch.index.store.Store;
@@ -65,7 +66,9 @@ public class RepositoriesServiceTests extends ESTestCase {
     @Override
     public void setUp() throws Exception {
         super.setUp();
+        ThreadContext threadContext = new ThreadContext(Settings.EMPTY);
         ThreadPool threadPool = mock(ThreadPool.class);
+        when(threadPool.getThreadContext()).thenReturn(threadContext);
         final TransportService transportService = new TransportService(
             Settings.EMPTY,
             mock(Transport.class),

test/framework/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreTestUtil.java

@@ -29,6 +29,8 @@
 import org.elasticsearch.common.blobstore.BlobContainer;
 import org.elasticsearch.common.blobstore.BlobMetadata;
 import org.elasticsearch.common.blobstore.BlobPath;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.common.xcontent.LoggingDeprecationHandler;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.index.snapshots.blobstore.BlobStoreIndexShardSnapshots;
@@ -417,7 +419,9 @@ public static ClusterService mockClusterService(RepositoryMetadata metadata) {
     }
 
     private static ClusterService mockClusterService(ClusterState initialState) {
+        final ThreadContext threadContext = new ThreadContext(Settings.EMPTY);
         final ThreadPool threadPool = mock(ThreadPool.class);
+        when(threadPool.getThreadContext()).thenReturn(threadContext);
         when(threadPool.executor(ThreadPool.Names.SNAPSHOT)).thenReturn(new SameThreadExecutorService());
         when(threadPool.generic()).thenReturn(new SameThreadExecutorService());
         when(threadPool.info(ThreadPool.Names.SNAPSHOT)).thenReturn(