Fix PHP8.5 deprecation warnings with ReflectionProperty::setAccessible()

[staabm]

fixes test errors:

PHPUnit 9.6.23 by Sebastian Bergmann and contributors.

Warning:       No code coverage driver available

PHP Deprecated:  Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect in phar:///home/runner/work/phpstan-src/phpstan-src/extension/vendor/phpstan/phpstan/phpstan.phar/src/Testing/TestCaseSourceLocatorFactory.php on line 73
...R
Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect in phar:///home/runner/work/phpstan-src/phpstan-src/extension/vendor/phpstan/phpstan/phpstan.phar/src/Testing/TestCaseSourceLocatorFactory.php on line 73
.....................................................         57 / 57 (100%)

Time: 00:52.874, Memory: 110.00 MB

There was 1 risky test:

1) PHPStan\Rules\BooleansInConditions\BooleanInBooleanAndRuleTest::testRule
Test code or tested code printed unexpected output: 
Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect in phar:///home/runner/work/phpstan-src/phpstan-src/extension/vendor/phpstan/phpstan/phpstan.phar/src/Testing/TestCaseSourceLocatorFactory.php on line 73

setAccessible is a no-op since 8.1 - see https://wiki.php.net/rfc/make-reflection-setaccessible-no-op

[phpstan-bot]

This pull request has been marked as ready for review.

[ondrejmirtes]

Thank you!