Update CHANGELOG for 4.1.2

Merge branch '4.0' into 4.1

Reset `Model::$unset` when a model is saved or refreshed (mongodb#2709)

* Override save() and refresh() functions to clear $this->unset
* Add tests reset Model::$unset when a model is saved or refreshed

---------

Co-authored-by: Richard Fila <“[email protected]”>
Co-authored-by: Jérôme Tamarelle <[email protected]>

Change release date

Release 4.0.2

Release 4.0.0

Release 4.0.0-rc1

Remove legacy from readme (mongodb#2586)

Remove legacy from readme (mongodb#2586)

fix: use correct package name when looking up version (mongodb#2511)