[php-src] Issue #20864: bug69442.phpt (PTY test) is flaky

Issue: https://github.com/php/php-src/issues/20864
Author: iluuu1994

### Description

ext/standard/tests/file/bug69442.phpt frequently fails in CI:

https://github.com/php/php-src/actions/runs/20802473279/job/59750077725

Resulted in this output:

```diff
- read from pipe 0: string(5) "foo
- "
+ read from pipe 0: string(0) ""
  read from pipe 3: string(3) "42
  "
```

But I expected this output instead:
```
No error
```

I've observed this on macOS and PPC64.

### PHP Version

```plain
Any supported version
```

### Operating System

_No response_