[CodeQuality] Use static Assert:: call for assert() inside anonymous class

[TomasVotruba]

Improves AssertFuncCallToPHPUnitAssertRector.

assert() inside an anonymous class has no test-case $this, so converting to $this->assertTrue() would call the method on the anonymous class instead of the TestCase. This now emits a static \PHPUnit\Framework\Assert::assertTrue() call instead, mirroring the existing static-closure handling.

Before

public function some($response)
{
    return new class($response) {
        public function __construct($response)
        {
            assert((bool) $response);
        }
    };
}

After

public function some($response)
{
    return new class($response) {
        public function __construct($response)
        {
            \PHPUnit\Framework\Assert::assertTrue((bool) $response);
        }
    };
}

Added fixture assert_inside_anonymous_class.php.inc.