### 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)


break;
							
							case Variant::RID:
							case Variant::BOOL:
							case Variant::CALLABLE:
							case Variant::FLOAT:
							case Variant::INT:
							case Variant::NIL:
							case Variant::NODE_PATH:
							case Variant::SIGNAL:
							case Variant::STRING_NAME:
								break;
							
							case Variant::DICTIONARY:
							case Variant::VARIANT_MAX:
								break;
						}
						if (error) {
							push_error(vformat(R"(Invalid index type "%s" for a base of type "%s".)", index_type.to_string(), base_type.to_string()), p_subscript->index);
						}
					}
				} else if (base_type.kind != GDScriptParser::DataType::BUILTIN && !index_type.is_variant()) {
					if (index_type.builtin_type != Variant::STRING && index_type.builtin_type != Variant::STRING_NAME) {
						push_error(vformat(R"(Only String or StringName can be used as index for type "%s", but received a "%s".)", base_type.to_string(), index_type.to_string()), p_subscript->index);
					}
				}
				
				result_type.builtin_type = Variant::NIL;
				result_type.kind = GDScriptParser::DataType::BUILTIN;
				result_type.type_source = base_type.is_hard_type() ? GDScriptParser::DataType::ANNOTATED_INFERRED : GDScriptParser::DataType::INFERRED;