Warnings mess up stdout

[geek-merlin]

The Story

$ vendor/bin/castor compile my-app.linux.phar -v
...
In CompileCommand.php line 287:
  [ErrorException]                                
  Warning: Trying to access array offset on null

The Offending Code

        $p = new Process([\PHP_BINARY, $input->getArgument('phar-path'), 'list', '--format', 'json']);
        $p->mustRun();
        $appName = json_decode($p->getOutput(), true)['application']['name'];

The Debugging

The process output has

• valid JSON
• Deprecation warning when repacking a PHAR with Castor (Symfony Console 7.4 add() deprecation) #772 warnings before it

The deeper problem

Fixing #772 will fix the problem, but it may be only a bandaid for a deeper problem: That warnings go to stdout and not stderr, torpedoing output parsing.