GDExtension godot-cpp checkout instructions points to 4.0 sources instead of 4.1 sources

[jtiai]

Your Godot version:
4.1

Issue description:

GDExtension page for checking out godot-cpp points to version 4,0 instead of 4.1 which later on causes building the extension itself to fail. Godot-cpp builds just fine with incorrect instructions.:

git submodule add -b 4.0 https://github.com/godotengine/godot-cpp

URL to the documentation page:

https://docs.godotengine.org/en/stable/tutorials/scripting/gdextension/gdextension_cpp_example.html#setting-up-the-project

[AThousandShips]

• Duplicate of Documentation for GDExtension in 4.1 still refers to 4.0 #7648

This was fixed in #7653 but hasn't been cherry picked yet

Thank you for reporting!