Setter example code is not up to date for Godot 4.1

[badunius]

Your Godot version: 4.1.1

Issue description:
There's green "up-to-date" banner on Godot notifications docs page, however example code in "_init vs. initialization vs. export" section uses setget instruction, and in the comments it is said that setting variable via self. calls a setter unlike setting it directly

URL to the documentation page:
https://docs.godotengine.org/en/stable/tutorials/best_practices/godot_notifications.html#process-vs-physics-process-vs-input

[jynus]

This was fixed on #8114 and #8293 for 4.2, it just requires backporting.

[skyace65]

The changes from both PRs jynus referenced are part of the stable docs now.