Updating to Godot 4.0 GDNative API for a first-party plugin

The GSoC work on the VCS integration improvement project over at https://github.com/godotengine/godot-git-plugin by janglee is almost complete and works with the 3.2 GDNative API.

However now the GDNative API in Godot 4.0 has changed in its core e.g. StringName has been added to the core, and some API endpoints have started using StringName. This means that our older way of just using the custom api.json from a Godot 4.0 build is not enough to begin testing the plugin on Godot 4.0. The build results in undefined symbol errors (most being for StringName apparently) when just using the custom API.

Is there a way to bypass this or do we have some documentation on how to update godot-cpp on our own to keep testing the plugin in 4.0 before Godot 4.0 is released?