To reproduce:
composer phpunit -- extensions/Translate/tests/phpunit/unit/messagegroups/SubsetMessageGroupTest.php
Output:
> phpunit 'extensions/Translate/tests/phpunit/unit/messagegroups/SubsetMessageGroupTest.php' Using PHP 8.1.20 Running without MediaWiki settings because there are no integration tests PHPUnit 9.5.28 by Sebastian Bergmann and contributors. .Invalid top messages: key-unknown .... 5 / 5 (100%) Time: 00:00.018, Memory: 16.00 MB OK (5 tests, 7 assertions)
This can also be seen in all CI runs that include Translate.
The test should be updated so that this warning isn't printed. Also, error_log is not generally used in MediaWiki. It should use a PSR logger instead.