### 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)


bool has_valid_setter = false;
				if (member.variable->getter_pointer != nullptr) {
					if (p_class->has_function(member.variable->getter_pointer->name)) {
						getter_function = p_class->get_member(member.variable->getter_pointer->name).function;
					}
					if (getter_function == nullptr) {
						push_error(vformat(R"(Getter "%s" not found.)", member.variable->getter_pointer->name), member.variable);
					} else {
						GDScriptParser::DataType return_datatype = getter_function->datatype;
						if (getter_function->return_type != nullptr) {
							return_datatype = getter_function->return_type->datatype;
							return_datatype.is_meta_type = false;
						}
						if (getter_function->parameters.size() != 0 || return_datatype.has_no_type()) {
							push_error(vformat(R"(Function "%s" cannot be used as getter because of its signature.)", getter_function->identifier->name), member.variable);
						} else if (!is_type_compatible(member.variable->datatype, return_datatype, true)) {
							push_error(vformat(R"(Function with return type "%s" cannot be used as getter for a property of type "%s".)", return_datatype.to_string(), member.variable->datatype.to_string()), member.variable);
						} else {
							has_valid_getter = true;
#ifdef DEBUG_ENABLED
							if (member.variable->datatype.builtin_type == Variant::INT && return_datatype.builtin_type == Variant::FLOAT) {
								parser->push_warning(member.variable, GDScriptWarning::NARROWING_CONVERSION);
							}
#endif
						}
					}
				}
				if (member.variable->setter_pointer != nullptr) {
					if (p_class->has_function(member.variable->setter_pointer->name)) {
						setter_function = p_class->get_member(member.variable->setter_pointer->name).function;