[12.x] Align casts property type with casts method return type

[nhedger]

Summary

This PR updates the PHPDoc type for the casts property in the HasAttributes trait so it matches the type used by the trait’s casts method.

framework/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php

Lines 1698 to 1706 in affb0bc

	/**
	* Get the attributes that should be cast.
	*
	* @return array<string, string>
	*/
	protected function casts()
	{
	return [];
	}

[shaedrich]

Wouldn't this ideally be something like this?

Suggested change

	* @var array<string, string>
	* @var array<string, string|class-string<\UnitEnum|\Illuminate\Contracts\Database\Eloquent\CastsAttributes|\Illuminate\Contracts\Database\Eloquent\Castable>>