### 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_error(R"(Cannot use "extends" more than once in the same class.)");
		}
		parse_extends();
		end_statement("superclass");
	}
	parse_class_body(multiline);
	complete_extents(n_class);
	if (multiline) {
		consume(GDScriptTokenizer::Token::DEDENT, R"(Missing unindent at the end of the class body.)");
	}
	current_class = previous_class;
	return n_class;
}
void GDScriptParser::parse_class_name() {
	if (consume(GDScriptTokenizer::Token::IDENTIFIER, R"(Expected identifier for the global class name after "class_name".)")) {
		current_class->identifier = parse_identifier();
		current_class->fqcn = String(current_class->identifier->name);
	}
	if (match(GDScriptTokenizer::Token::EXTENDS)) {
		
		parse_extends();
		end_statement("superclass");
	} else {
		end_statement("class_name statement");
	}
}
void GDScriptParser::parse_extends() {
	current_class->extends_used = true;
	int chain_index = 0;
	if (match(GDScriptTokenizer::Token::LITERAL)) {