getFunctions() should return array, not iterable

[tacman]

I bumped to Symfony 6.4 beta 3, and the getFunctions() function throws an error because the Symfony interface now expects an array. Before, it did not have a return type.

interface ExpressionFunctionProviderInterface
{
    /**
     * @return ExpressionFunction[]
     */
    public function getFunctions(): array;
}

https://github.com/StenopePHP/Stenope/blob/master/src/ExpressionLanguage/ExpressionLanguageProvider.php