Process Isolation does not work when PHPUnit is used as PHAR

[bugreportuser]

Q	A
PHPUnit version	7.4.3
PHP version	7.2.10
Installation Method	PHAR

This is related to #3367 and #3306.

When --process-isolation is added, no assertions run using the PHAR. If composer is used, the output is correct with or without process isolation.

Class isolation has the same output because of #3258.

FailTest.php:

<?php
class FailTest extends PHPUnit\Framework\TestCase {
    public function testFail () {
        $this->assertTrue(false);
    }
}

No process isolation:

$ ./phpunit FailTest.php
PHPUnit 7.4.3 by Sebastian Bergmann and contributors.

F                                                                   1 / 1 (100%)

Time: 52 ms, Memory: 10.00MB

There was 1 failure:

1) FailTest::testFail
Failed asserting that false is true.

/home/.../phpunit/FailTest.php:4

FAILURES!
Tests: 1, Assertions: 1, Failures: 1.

Process isolation:

$ ./phpunit FailTest.php --process-isolation
PHPUnit 7.4.3 by Sebastian Bergmann and contributors.

.                                                                   1 / 1 (100%)

Time: 123 ms, Memory: 10.00MB

OK (1 test, 0 assertions)

[sebastianbergmann]

I was able to reproduce the issue.