[php-src] Issue #22292: AST pretty printing does not correctly handle invalid variable names

Issue: https://github.com/php/php-src/issues/22292
Author: TimWolla

### Description

The following code:

```php
<?php

class Foo {
	public function __get($name) { return $name; }
}

${'---'} = 'foo';
try {
	assert(!${'---'});
} catch (Error $e) {
	echo $e->getMessage(), PHP_EOL;
}

$f = new Foo();
try {
	assert(!$f->{'---'});
} catch (Error $e) {
	echo $e->getMessage(), PHP_EOL;
}
```

Resulted in this output:
```
assert(!${---})
assert(!$f->{---})
```

But I expected this output instead:
```
assert(!${'---'})
assert(!$f->{'---'})
```


### PHP Version

```plain
PHP 8.4.23-dev (cli) (built: Jun 13 2026 14:48:42) (NTS DEBUG)
Copyright (c) The PHP Group
Zend Engine v4.4.23-dev, Copyright (c) Zend Technologies
```

### Operating System

_No response_