Fix flaky test rabbit_mqtt_qos0_queue_overflow

The test always succeeds on `main` branch.

The test also always succeeds on `mc` branch when running remotely:
```
bazel test //deps/rabbitmq_mqtt:reader_SUITE --test_env FOCUS="-group tests -case rabbit_mqtt_qos0_queue_overflow" --config=rbe-25 -t- --runs_per_test=50
```

However, the test flakes when running on `mc` branch locally on the MAC:
```
make -C deps/rabbitmq_mqtt ct-reader t=tests:rabbit_mqtt_qos0_queue_overflow FULL=1
```
with the following local changes:
```
~/workspace/rabbitmq-server/deps/rabbitmq_mqtt mc *6 !1 >                                                                                                                                                                                                                                                  3s direnv rb 2.7.2
diff --git a/deps/rabbitmq_mqtt/test/reader_SUITE.erl b/deps/rabbitmq_mqtt/test/reader_SUITE.erl
index fb71eae375..21377a2e73 100644
--- a/deps/rabbitmq_mqtt/test/reader_SUITE.erl
+++ b/deps/rabbitmq_mqtt/test/reader_SUITE.erl
@@ -27,7 +27,7 @@ all() ->

 groups() ->
     [
-     {tests, [],
+     {tests, [{repeat_until_any_fail, 30}],
       [
        block_connack_timeout,
        handle_invalid_packets,
@@ -43,7 +43,7 @@ groups() ->
     ].

 suite() ->
-    [{timetrap, {seconds, 60}}].
+    [{timetrap, {minutes, 60}}].

 %% -------------------------------------------------------------------
 %% Testsuite setup/teardown.
```
failes prior to this commit after the 2nd time and does not fail after
this commit.

1 files changed, 2 insertions, 2 deletions

diff --git a/deps/rabbitmq_mqtt/test/reader_SUITE.erl b/deps/rabbitmq_mqtt/test/reader_SUITE.erl
index fb71eae375..1f5ba05d98 100644
--- a/deps/rabbitmq_mqtt/test/reader_SUITE.erl
+++ b/deps/rabbitmq_mqtt/test/reader_SUITE.erl
@@ -247,7 +247,7 @@ rabbit_mqtt_qos0_queue_overflow(Config) ->
     ok = rabbit_ct_broker_helpers:enable_feature_flag(Config, rabbit_mqtt_qos0_queue),
 
     Topic = atom_to_binary(?FUNCTION_NAME),
-    Msg = binary:copy(<<"x">>, 1000),
+    Msg = binary:copy(<<"x">>, 2000),
     NumMsgs = 10_000,
 
     %% Provoke TCP back-pressure from client to server by using very small buffers.
@@ -269,7 +269,7 @@ rabbit_mqtt_qos0_queue_overflow(Config) ->
                   end, lists:seq(1, NumMsgs)),
 
     %% Give the server some time to process (either send or drop) the messages.
-    timer:sleep(2000),
+    timer:sleep(2500),
 
     %% Let's resume the receiving client to receive any remaining messages that did
     %% not get dropped.