docs: fix Project Files changes

See https://forum.codeigniter.com/showthread.php?tid=91656&pid=421265#pid421265

Author: kenjis

user_guide_src/source/installation/upgrade_455.rst

@@ -32,12 +32,12 @@ and it is recommended that you merge the updated versions with your application:
 Config
 ------
 
-- composer.json
+- preload.php
 
 All Changes
 ===========
 
 This is a list of all files in the **project space** that received changes;
 many will be simple comments or formatting that have no effect on the runtime:
 
-- composer.json
+- preload.php