Prevent argument unpacking iterable with non-array-key key

[AndrolGenhald]

Iterables have scalar keys, this means when unpacking an iterable when calling a function psalm should show an issue if the key isn't an int or a string.
https://psalm.dev/r/c6f65aebef
https://3v4l.org/Y8Vbu

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/c6f65aebef

<?php

/**
 * @template TValue
 * @implements Iterator<float, TValue>
 */
class FloatKeyIterator implements Iterator
{
    /** @var int */
    private $position = 0;
    /** @var list<array{float, TValue}> */
    private $data = [];
    
    /** @param list<array{float, TValue}> $data */
    public function __construct($data)
    {
        $this->data = $data;
    }
    
    /** @return TValue */
    public function current()
    {
        return $this->data[$this->position][1];
    }
    
    /** @return float */
    public function key()
    {
        return $this->data[$this->position][0];
    }
    
    public function next(): void
    {
        ++$this->position;
    }
    
    public function rewind(): void
    {
        $this->position = 0;
    }
    
    public function valid(): bool
    {
        return isset($this->data[$this->position]);
    }
}

/** @psalm-suppress UnusedParam */
function foo(string ...$args): void {}

/** @var FloatKeyIterator<string> */
$test = new FloatKeyIterator([[3.14, 'pi'], [2.72, 'e']]);
foo(...$test);

Psalm output (using commit 9f3f420):

No issues!