### Godot version

4.1.beta3

### System information

Fedora Workstation 38 - Godot 4.1.beta3 - Vulkan (Forward+)

### Issue description

**This is an issue created by the production team, we're working on it**

Currently, it's impossible to call virtual functions within GDScript.

This currently returns an error:
```gdscript
# a.gd
extends Node

func _process(delta: float) -> void:
	pass
```

```gdscript
# main.gd
extends Node

var my_node: Node = preload("res://a.gd").new()

func _process(delta: float) -> void:
	my_node._process(delta)  # Cannot call virtual function "_process()" because it hasn't been defined.
```

### Steps to reproduce

1. Create a script (`a.gd`) based on `Node` that declares `_process()`;
2. Create a main node;
3. Attach a script to the main node;
4. Initialize a variable with a new `a.gd` instance;
5. Try to run `_process()` on that node;
6. Find out that it returns an error.

### Minimal reproduction project

[virtual_functions.zip (updated)](https://github.com/godotengine/godot/files/11823992/virtual_functions.zip)


downgrades_assigned = !assigned_is_hard;
		}
	}
	p_assignment->set_datatype(op_type);
	if (assignee_is_variant) {
		if (!assignee_is_hard) {
			
			mark_node_unsafe(p_assignment);
		}
	} else {
		if (assignee_is_hard && !assigned_is_hard) {
			
			mark_node_unsafe(p_assignment);
			p_assignment->use_conversion_assign = true;
			downgrades_assigned = downgrades_assigned || (!assigned_is_variant && !is_type_compatible(assignee_type, op_type, true, p_assignment->assigned_value));
		} else if (compatible) {
			if (op_type.is_variant()) {
				
				mark_node_unsafe(p_assignment);
				if (assignee_is_hard) {
					
					p_assignment->use_conversion_assign = true;
				} else {
					
					downgrades_assignee = true;
				}
			} else if (!is_type_compatible(assignee_type, op_type, assignee_is_hard, p_assignment->assigned_value)) {
				
				mark_node_unsafe(p_assignment);
				if (assignee_is_hard) {