### 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(p_assignable, GDScriptWarning::INFERENCE_ON_VARIANT, p_kind);
			}
#endif
		} else {
			if (!initializer_type.is_set()) {
				push_error(vformat(R"(Could not resolve type for %s "%s".)", p_kind, p_assignable->identifier->name), p_assignable->initializer);
			}
		}
		if (!has_specified_type) {
			type = initializer_type;
			if (!type.is_set() || (type.is_hard_type() && type.kind == GDScriptParser::DataType::BUILTIN && type.builtin_type == Variant::NIL && !is_constant)) {
				type.kind = GDScriptParser::DataType::VARIANT;
			}
			if (p_assignable->infer_datatype || is_constant) {
				type.type_source = GDScriptParser::DataType::ANNOTATED_INFERRED;
			} else {
				type.type_source = GDScriptParser::DataType::INFERRED;
			}
		} else if (!specified_type.is_variant()) {
			if (initializer_type.is_variant() || !initializer_type.is_hard_type()) {
				mark_node_unsafe(p_assignable->initializer);
				p_assignable->use_conversion_assign = true;
				if (!initializer_type.is_variant() && !is_type_compatible(specified_type, initializer_type, true, p_assignable->initializer)) {
					downgrade_node_type_source(p_assignable->initializer);
				}
			} else if (!is_type_compatible(specified_type, initializer_type, true, p_assignable->initializer)) {
				if (!is_constant && is_type_compatible(initializer_type, specified_type)) {
					mark_node_unsafe(p_assignable->initializer);
					p_assignable->use_conversion_assign = true;
				} else {