docs: add v4.2.9 changelog

[kenjis]

Description

• add missing changelog

Checklist:

• Securely signed commits
• [] Component(s) with PHPDoc blocks, only if necessary or adds value
• [] Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[Terrorboy]

https://github.com/codeigniter4/CodeIgniter4/blob/develop/system/CodeIgniter.php#L50

Version modify plz

@MGatner

[MGatner]

Thanks @Terrorboy. I hotfixed 4.2.9 so didn't take it through the regular process. I can see how this is confusing; maybe in the future hotfixes should be 4.2.8.1 style or something. For now in order to fix it we would need another release so unless the team overwhelmingly thinks otherwise I say we just leave it.