[php-src] Issue #22291: AST pretty printing does not correctly handle braces in string interpolation

Issue: https://github.com/php/php-src/issues/22291
Author: TimWolla

### Description

The following code:

```php
<?php

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

Resulted in this output:
```
string(5) "{abc}"
string(3) "abc"
assert(!"{$foo}")
```

But I expected this output instead:
```
string(5) "{abc}"
string(3) "abc"
assert(!"{{$foo}}")
```


### PHP Version

```plain
PHP 8.6.0-dev (cli) (built: Jun 13 2026 14:01:23) (NTS DEBUG)
Copyright © The PHP Group and Contributors
Zend Engine v4.6.0-dev, Copyright © Zend by Perforce
    with Zend OPcache v8.6.0-dev, Copyright ©, by Zend by Perforce
```

### Operating System

_No response_