Signal cannot be attached to plugin node

[tavurth]

Godot version:

OS/device including version:

Issue description:

When using a custom plugin node, signals cannot be addressed as inbound to that script, as seen in the screenshot below, the plugin node is greyed out, and cannot be selected.

Steps to reproduce:

1. Create an EditorPlugin, which adds a custom type (add_custom_type)
2. Create an instance of that custom node type
3. Try to address a signal to that node

Minimal reproduction project:
https://github.com/tavurth/godot-signal-bug

Workarounds
You can add the signal as normal if you double click on the node (which is greyed out)

[tavurth]

Additionally, when the user has another selectable node at the same tree as an addon node, the addon node cannot be selected as the target of a signal even by double clicking.

When I attempt to connect to the AddonB node, the signal appears in the NormalNode's source and is connected in that way too.

[tavurth]

Note: The workaround I have for this is to click advanced mode in the signal selector window.

This will then allow you to select the plugin node.

[tavurth]

This is resolved in Godot v4.4.1.stable.official [49a5bc7].

The plugin node is greyed out, but can be selected, and the signal connected (which creates a function).