1 ``typo3/cms-composer-installers`` v4.x got installed, which moves__ the sysext extension directory from typo3/sysext/ to vendor/typo3/. TYPO3's own bootstrap didn't like that with unit tests.
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3 __ https://docs.typo3.org/m/typo3/reference-coreapi/11.5/en-us/ApiOverview/DirectoryStructure/Index.html#composer-installer-v4