### 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("Assert ( ");
	print_expression(p_assert->condition);
	push_line(" )");
}
void GDScriptParser::TreePrinter::print_assignment(AssignmentNode *p_assignment) {
	switch (p_assignment->assignee->type) {
		case Node::IDENTIFIER:
			print_identifier(static_cast<IdentifierNode *>(p_assignment->assignee));
			break;
		case Node::SUBSCRIPT:
			print_subscript(static_cast<SubscriptNode *>(p_assignment->assignee));
			break;
		default:
			break; 
	}
	push_text(" ");
	switch (p_assignment->operation) {
		case AssignmentNode::OP_ADDITION:
			push_text("+");
			break;
		case AssignmentNode::OP_SUBTRACTION:
			push_text("-");
			break;
		case AssignmentNode::OP_MULTIPLICATION:
			push_text("*");
			break;
		case AssignmentNode::OP_DIVISION:
			push_text("/");