Avoid leaking blackholed register ops in tests (elastic#114287)

Today when we reboot a node in a test case derived from
`AbstractCoordinatorTestCase` we lose the contents of
`blackholedRegisterOperations`, but it's important that these operations
_eventually_ run. With this commit we copy these operations over into
the new node.

Author: DaveCTurner

test/framework/src/main/java/org/elasticsearch/cluster/coordination/AbstractCoordinatorTestCase.java

@@ -1250,7 +1250,7 @@ ClusterNode restartedNode(
                     .roles(localNode.isMasterNode() && DiscoveryNode.isMasterNode(settings) ? ALL_ROLES_EXCEPT_VOTING_ONLY : emptySet())
                     .build();
                 try {
-                    return new ClusterNode(
+                    final var restartedNode = new ClusterNode(
                         nodeIndex,
                         newLocalNode,
                         (node, threadPool) -> createPersistedStateFromExistingState(
@@ -1263,6 +1263,8 @@ ClusterNode restartedNode(
                         settings,
                         nodeHealthService
                     );
+                    restartedNode.blackholedRegisterOperations.addAll(blackholedRegisterOperations);
+                    return restartedNode;
                 } finally {
                     clearableRecycler.clear();
                 }