Fix test flake

Prior to this commit, test
```
ERL_AFLAGS="+S 2" make -C deps/rabbit ct-amqp_client t=cluster_size_3:detach_requeues_two_connections_quorum_queue
```
failed rarely locally, and more often in CI.
An instance of a failed test in CI is
https://github.com/rabbitmq/rabbitmq-server/actions/runs/10298099899/job/28502687451?pr=11945

The test failed with:
```
=== === Reason: {assertEqual,[{module,amqp_client_SUITE},
                               {line,2800},
                               {expression,"amqp10_msg : body ( Msg1 )"},
                               {expected,[<<"1">>]},
                               {value,[<<"2">>]}]}
  in function  amqp_client_SUITE:detach_requeues_two_connections/2 (amqp_client_SUITE.erl, line 2800)
```
because it could happen that Receiver1's credit top up to the quorum
queue is applied before Receiver0's credit top up such that Receiver1
gets enqueued to the ServiceQueue before Receiver0.

Author: ansd

deps/rabbit/test/amqp_client_SUITE.erl

@@ -2767,6 +2767,7 @@ detach_requeues_two_connections(QType, Config) ->
     {ok, LinkPair} = rabbitmq_amqp_client:attach_management_link_pair_sync(Session1, <<"my link pair">>),
     QProps = #{arguments => #{<<"x-queue-type">> => {utf8, QType}}},
     {ok, #{type := QType}} = rabbitmq_amqp_client:declare_queue(LinkPair, QName, QProps),
+    flush(link_pair_attached),
 
     %% Attach 1 sender and 2 receivers.
     {ok, Sender} = amqp10_client:attach_sender_link(Session0, <<"sender">>, Address, settled),
@@ -2778,13 +2779,16 @@ detach_requeues_two_connections(QType, Config) ->
     end,
     ok = gen_statem:cast(Session0, {flow_session, #'v1_0.flow'{incoming_window = {uint, 1}}}),
     ok = amqp10_client:flow_link_credit(Receiver0, 50, never),
+    %% Wait for credit being applied to the queue.
+    timer:sleep(10),
 
     {ok, Receiver1} = amqp10_client:attach_receiver_link(Session1, <<"receiver 1">>, Address, unsettled),
     receive {amqp10_event, {link, Receiver1, attached}} -> ok
     after 5000 -> ct:fail({missing_event, ?LINE})
     end,
-    ok = amqp10_client:flow_link_credit(Receiver1, 50, never),
-    flush(attached),
+    ok = amqp10_client:flow_link_credit(Receiver1, 40, never),
+    %% Wait for credit being applied to the queue.
+    timer:sleep(10),
 
     NumMsgs = 6,
     [begin