subscription/015_stream sometimes breaks

Hi,

A couple of times a day, cfbot reports an error like this:

https://cirrus-ci.com/task/6424286882168832

I didn't study it closely but it looks like there might be a second
deadlock, after the one that is expected by the test?  Examples from
the past couple of weeks:

cfbot=> select test.task_id, task.task_name, task.created as time from
test join task using (task_id) where suite = 'subscription' and name =
'015_stream' and result = 'ERROR' and task.created > now() - interval
'14 days' order by task.created desc;
     task_id      |                   task_name
------------------+------------------------------------------------
 6600867550330880 | Windows - Server 2019, VS 2019 - Meson & ninja
 6222795470798848 | Windows - Server 2019, VS 2019 - Meson & ninja
 6162088322662400 | macOS - Ventura - Meson
 5014781862608896 | Windows - Server 2019, VS 2019 - Meson & ninja
 6424286882168832 | Windows - Server 2019, VS 2019 - Meson & ninja
 6683705222103040 | Windows - Server 2019, VS 2019 - Meson & ninja
 5881665076068352 | Windows - Server 2019, VS 2019 - Meson & ninja
 5865929054093312 | Windows - Server 2019, VS 2019 - Meson & ninja
 5855144995192832 | Windows - Server 2019, VS 2019 - Meson & ninja
 6071567994585088 | Windows - Server 2019, VS 2019 - Meson & ninja
 5311312343859200 | Windows - Server 2019, VS 2019 - Meson & ninja
 4986100071006208 | FreeBSD - 13 - Meson
 6302301388800000 | Windows - Server 2019, VS 2019 - Meson & ninja
 4554627119579136 | Windows - Server 2019, VS 2019 - Meson & ninja
 6106090807492608 | Windows - Server 2019, VS 2019 - Meson & ninja
 5190113534148608 | Windows - Server 2019, VS 2019 - Meson & ninja
 6452324697112576 | Windows - Server 2019, VS 2019 - Meson & ninja
 4610228927332352 | Windows - Server 2019, VS 2019 - Meson & ninja
 4928567608344576 | Windows - Server 2019, VS 2019 - Meson & ninja
 5705451157848064 | FreeBSD - 13 - Meson
 5952066133164032 | Windows - Server 2019, VS 2019 - Meson & ninja
 5341101565935616 | Windows - Server 2019, VS 2019 - Meson & ninja
 6751165837213696 | Windows - Server 2019, VS 2019 - Meson & ninja
 4624168109473792 | Windows - Server 2019, VS 2019 - Meson & ninja
 6730863963013120 | Windows - Server 2019, VS 2019 - Meson & ninja
 6174140269330432 | Windows - Server 2019, VS 2019 - Meson & ninja
 4637318561136640 | Windows - Server 2019, VS 2019 - Meson & ninja
 4535300303618048 | Windows - Server 2019, VS 2019 - Meson & ninja
 5672693542944768 | FreeBSD - 13 - Meson
 6087381225308160 | Windows - Server 2019, VS 2019 - Meson & ninja
 6098413217906688 | Windows - Server 2019, VS 2019 - Meson & ninja
 6130601380544512 | Windows - Server 2019, VS 2019 - Meson & ninja
 5546054284738560 | Windows - Server 2019, VS 2019 - Meson & ninja
 6674258676416512 | Windows - Server 2019, VS 2019 - Meson & ninja
 4571976740634624 | FreeBSD - 13 - Meson
 6566515328155648 | Windows - Server 2019, VS 2019 - Meson & ninja
 6576879084240896 | Windows - Server 2019, VS 2019 - Meson & ninja
 5295804827566080 | Windows - Server 2019, VS 2019 - Meson & ninja
 6426387188285440 | Windows - Server 2019, VS 2019 - Meson & ninja
 4763275859066880 | Windows - Server 2019, VS 2019 - Meson & ninja
 6137227240013824 | Windows - Server 2019, VS 2019 - Meson & ninja
 5185063273365504 | Windows - Server 2019, VS 2019 - Meson & ninja
 6542656449282048 | Windows - Server 2019, VS 2019 - Meson & ninja
 4874919171850240 | Windows - Server 2019, VS 2019 - Meson & ninja
 6531290556530688 | Windows - Server 2019, VS 2019 - Meson & ninja
 5377848232378368 | FreeBSD - 13 - Meson
 6436049925177344 | FreeBSD - 13 - Meson
 6057679748071424 | Windows - Server 2019, VS 2019 - Meson & ninja
 5534694867992576 | Windows - Server 2019, VS 2019 - Meson & ninja
 4831311429369856 | Windows - Server 2019, VS 2019 - Meson & ninja
 4704271531245568 | macOS - Ventura - Meson
 5297047549509632 | Windows - Server 2019, VS 2019 - Meson & ninja
 5836487120388096 | macOS - Ventura - Meson
 6527459915464704 | FreeBSD - 13 - Meson
 4985483743199232 | FreeBSD - 13 - Meson
 4583651082502144 | Linux - Debian Bullseye - Meson
 5498444756811776 | FreeBSD - 13 - Meson
 5146601035923456 | Windows - Server 2019, VS 2019 - Meson & ninja
 5709550989344768 | macOS - Ventura - Meson
 6357936616767488 | FreeBSD - 13 - Meson
(60 rows)