Update tests to use more strict data types instead of mixed.

tests/unicode_characters.aer

@@ -1,8 +1,8 @@
 class Unicode {
 
 	public function unicon(string $str, bool $to_uni = true) {
-		mixed $cpp;
-		mixed $cp = array('А' => 'А', 'а' => 'а',
+		string $cpp;
+		string[] $cp = array('А' => 'А', 'а' => 'а',
 			"Б" => "Б", "б" => "б",
 			"В" => "В", "в" => "в",
 			"Г" => "Г", "г" => "г",