### 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)


parser->push_warning(member.variable, GDScriptWarning::ONREADY_WITH_EXPORT);
				}
				if (member.variable->initializer) {
					
					
					if (!member.variable->is_static && !member.variable->onready && member.variable->initializer && (member.variable->initializer->type == GDScriptParser::Node::GET_NODE || member.variable->initializer->type == GDScriptParser::Node::CALL || member.variable->initializer->type == GDScriptParser::Node::CAST)) {
						GDScriptParser::Node *expr = member.variable->initializer;
						if (expr->type == GDScriptParser::Node::CAST) {
							expr = static_cast<GDScriptParser::CastNode *>(expr)->operand;
						}
						bool is_get_node = expr->type == GDScriptParser::Node::GET_NODE;
						bool is_using_shorthand = is_get_node;
						if (!is_get_node && expr->type == GDScriptParser::Node::CALL) {
							is_using_shorthand = false;
							GDScriptParser::CallNode *call = static_cast<GDScriptParser::CallNode *>(expr);
							if (call->function_name == SNAME("get_node")) {
								switch (call->get_callee_type()) {
									case GDScriptParser::Node::IDENTIFIER: {
										is_get_node = true;
									} break;
									case GDScriptParser::Node::SUBSCRIPT: {
										GDScriptParser::SubscriptNode *subscript = static_cast<GDScriptParser::SubscriptNode *>(call->callee);
										is_get_node = subscript->is_attribute && subscript->base->type == GDScriptParser::Node::SELF;
									} break;
									default:
										break;
								}
							}
						}
						if (is_get_node) {