core functional tests does not work if checkout directory is called 'typo3'

[lolli42]

git clone https://github.com/typo3/typo3
cd typo3
Build/Scripts/runTests.sh -s composerInstall
Build/Scripts/runTests.sh -x -s functional typo3/sysext/core/Tests/Functional/Authentication/AbstractUserAuthenticationTest.php

->

1) TYPO3\CMS\Core\Tests\Functional\Authentication\AbstractUserAuthenticationTest::pushModuleDataDoesNotRevealPlainSessionId
Error: Call to a member function getRealPath() on null

/var/www/local/git/typo3/vendor/typo3/testing-framework/Classes/Core/Testbase.php:369
/var/www/local/git/typo3/vendor/typo3/testing-framework/Classes/Core/Functional/FunctionalTestCase.php:340
/var/www/local/git/typo3/bin/phpunit:122

This only happens if the project is cloned to a directory name called typo3. if cloning to typo3-foo, all is fine.