Fix PHP 7.4 build

[staabm]

fixes

1) PHPStan\Analyser\AnalyserIntegrationTest::testBug14604
Failed asserting that actual size 4 matches expected size 0.

Emitted errors:
- Throw expression is supported only on PHP 8.0 and later
  in /home/runner/work/phpstan-src/phpstan-src/tests/PHPStan/Analyser/data/bug-14604.php on line 11

- Throw expression is supported only on PHP 8.0 and later
  in /home/runner/work/phpstan-src/phpstan-src/tests/PHPStan/Analyser/data/bug-14604.php on line 17

- Throw expression is supported only on PHP 8.0 and later
  in /home/runner/work/phpstan-src/phpstan-src/tests/PHPStan/Analyser/data/bug-14604.php on line 29

- Throw expression is supported only on PHP 8.0 and later
  in /home/runner/work/phpstan-src/phpstan-src/tests/PHPStan/Analyser/data/bug-14604.php on line 45

/home/runner/work/phpstan-src/phpstan-src/src/Testing/PHPStanTestCase.php:158
/home/runner/work/phpstan-src/phpstan-src/tests/PHPStan/Analyser/AnalyserIntegrationTest.php:206
/home/runner/work/phpstan-src/phpstan-src/tests/vendor/phpunit/phpunit/src/TextUI/Command.php:146