[CodeQuality] Skip by-ref use() closures in CallbackSingleAssertToSimplerRector

[TomasVotruba]

CallbackSingleAssertToSimplerRector wrongly rewrote callbacks that capture a variable by reference in use. Such a variable is typically mutated in an earlier callback, so freezing it into an equalTo() matcher captures the wrong value.

Now the rule skips any callback closure with a by-reference use.

$download = null;

$this->entityManager->expects($this->once())
    ->method('persist')
    ->with($this->callback(function ($downloadPersist) use (&$download): bool {
        $download = $downloadPersist;
        $this->assertInstanceOf(Download::class, $download);

        return true;
    }));

// referenced value modified above, must NOT be collapsed
$this->entityManager->expects($this->once())
    ->method('detach')
    ->with($this->callback(function ($downloadDetach) use (&$download): bool {
        $this->assertSame($downloadDetach, $download);

        return true;
    }));

Previously the second callback was rewritten to ->with($this->equalTo($downloadDetach)), which is wrong. Now it is left untouched.