Unit tests fail with PHP 7.4

[TiSiE]

PHPUnit 8.0.6 by Sebastian Bergmann and contributors.

............E...................................PHP Fatal error:  During class fetch: Uncaught Array and string offset access syntax with curly braces is deprecated

/home/mathias/projects/phpunit-utils/src/TestCase/SetupTargetTrait.php:130
/home/mathias/projects/phpunit-utils/test/TestUtilsTest/TestCase/SetupTargetTraitTest.php:33
 in /home/mathias/projects/phpunit-utils/test/TestUtilsTest/TestCase/SetupTargetTraitTest.php on line 33
PHP Stack trace:
PHP   1. {main}() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/phpunit:0
PHP   2. PHPUnit\TextUI\Command::main() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/phpunit:61
PHP   3. PHPUnit\TextUI\Command->run() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/src/TextUI/Command.php:164
PHP   4. PHPUnit\TextUI\TestRunner->doRun() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/src/TextUI/Command.php:208
PHP   5. PHPUnit\Framework\TestSuite->run() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/src/TextUI/TestRunner.php:595
PHP   6. PHPUnit\Framework\TestSuite->run() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/src/Framework/TestSuite.php:761
PHP   7. Cross\TestUtilsTest\TestCase\SetupTargetTraitTest->run() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/src/Framework/TestSuite.php:761
PHP   8. PHPUnit\Framework\TestResult->run() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/src/Framework/TestCase.php:795
PHP   9. Cross\TestUtilsTest\TestCase\SetupTargetTraitTest->runBare() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/src/Framework/TestResult.php:685
PHP  10. Cross\TestUtilsTest\TestCase\SetupTargetTraitTest->runTest() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/src/Framework/TestCase.php:841
PHP  11. Cross\TestUtilsTest\TestCase\SetupTargetTraitTest->testSetupCallsSetupTarget() /home/mathias/projects/phpunit-utils/vendor/phpunit/phpunit/src/Framework/TestCase.php:1152

Unfortunately, if used with PHP 7.4, PHPUnit will always produce this error, if SetupTargetTrait is used.