Intermittent unit test failure - assertCount() must be a countable or iterable

[golenkovm]

The following was thrown in one of the builds:

There was 1 error:

1) tool_dataflows\tool_dataflows_event_processor_test::test_process_event_immediate
PHPUnit\Framework\InvalidArgumentException: Argument #2 of PHPUnit\Framework\Assert::assertCount() must be a countable or iterable

/var/www/site/admin/tool/dataflows/tests/tool_dataflows_event_processor_test.php:199
/var/www/site/lib/phpunit/classes/advanced_testcase.php:80

ERRORS!
Tests: 4890, Assertions: 29196, Errors: 1, Skipped: 25.

Env details:

Moodle 4.1.15+ (Build: 20250124)
Php: 8.1.2.1.2.20, pgsql: 14.15 (Debian 14.15-1.pgdg120+1), OS: Linux 6.8.0-1021-aws x86_64
PHPUnit 9.5.28
Plugin branch MOODLE_401_STABLE
Plugin hash 64e587ae5e5554a390e824c878171acc9d2abc5d

Testing this in a local devbox didn't confirm the issue. Re-running in GoCD surprisingly self-healed the issue (the test passed). Raising this in case it will explode somewhere else.