Use notSame instead of notEq for stringNotEmpty (#336)

Author: kamil-zacek

src/Assert.php

@@ -65,7 +65,7 @@ public static function string(mixed $value, string $message = ''): string
     public static function stringNotEmpty(mixed $value, string $message = ''): string
     {
         static::string($value, $message);
-        static::notEq($value, '', $message);
+        static::notSame($value, '', $message);
 
         return $value;
     }