### Godot version

4.0 stable

### System information

Fedora, RX 590

### Issue description

I made a dictionary, and instead of using `:` to separate between key and value, i accidentally used `=`.
The error message was not clear at all `Parse Error: Expected identifier or string as LUA-style dictionary key.` 

I don't think assuming that people know how dictionaries are made in LUA is reasonable. And if this is not about LUA the programming language, i don't even know what this is about :D

I think this error should be replaced with something of the sort "Please use `:` as separator instead of `=` in your dictionary"

### Steps to reproduce

Paste this code in a script:

```

var dict = {
	1 = "lala"
}
```

Observe the error message
![image](https://user-images.githubusercontent.com/7917475/224549538-38ea25aa-ba75-431e-868b-0733a53b90ad.png)


### Minimal reproduction project

see above
push_text("Self(");
	if (p_self->current_class->identifier != nullptr) {
		print_identifier(p_self->current_class->identifier);
	} else {
		push_text("<main class>");
	}
	push_text(")");
}
void GDScriptParser::TreePrinter::print_signal(SignalNode *p_signal) {
	push_text("Signal ");
	print_identifier(p_signal->identifier);
	push_text("( ");
	for (int i = 0; i < p_signal->parameters.size(); i++) {
		print_parameter(p_signal->parameters[i]);
	}
	push_line(" )");
}
void GDScriptParser::TreePrinter::print_subscript(SubscriptNode *p_subscript) {
	print_expression(p_subscript->base);
	if (p_subscript->is_attribute) {
		push_text(".");
		print_identifier(p_subscript->attribute);
	} else {
		push_text("[ ");
		print_expression(p_subscript->index);
		push_text(" ]");
	}
}
void GDScriptParser::TreePrinter::print_statement(Node *p_statement) {