### 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)


if (p_source.kind == GDScriptParser::DataType::BUILTIN && p_source.builtin_type == Variant::INT) {
#ifdef DEBUG_ENABLED
			if (p_source_node) {
				parser->push_warning(p_source_node, GDScriptWarning::INT_AS_ENUM_WITHOUT_CAST);
			}
#endif
			return true;
		}
		if (p_source.kind == GDScriptParser::DataType::ENUM) {
			if (p_source.native_type == p_target.native_type) {
				return true;
			}
		}
		return false;
	}
	
	if (p_source.kind == GDScriptParser::DataType::BUILTIN && p_source.builtin_type == Variant::NIL) {
		
		return true;
	}
	StringName src_native;
	Ref<Script> src_script;
	const GDScriptParser::ClassNode *src_class = nullptr;
	switch (p_source.kind) {
		case GDScriptParser::DataType::NATIVE:
			if (p_target.kind != GDScriptParser::DataType::NATIVE) {
				
				return false;
			}
			if (p_source.is_meta_type) {