### 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
SubscriptNode *attribute = static_cast<SubscriptNode *>(call->callee);
			if (attribute->is_attribute) {
				if (attribute->attribute) {
					call->function_name = attribute->attribute->name;
				}
				make_completion_context(COMPLETION_ATTRIBUTE_METHOD, call->callee);
			} else {
				
				push_error(R"*(Cannot call on an expression. Use ".call()" if it's a Callable.)*");
			}
		} else {
			push_error(R"*(Cannot call on an expression. Use ".call()" if it's a Callable.)*");
		}
	}
	
	CompletionType ct = COMPLETION_CALL_ARGUMENTS;
	if (call->function_name == SNAME("load")) {
		ct = COMPLETION_RESOURCE_PATH;
	}
	push_completion_call(call);
	int argument_index = 0;
	do {
		make_completion_context(ct, call, argument_index++, true);
		if (check(GDScriptTokenizer::Token::PARENTHESIS_CLOSE)) {
			
			break;
		}
		bool use_identifier_completion = current.cursor_place == GDScriptTokenizer::CURSOR_END || current.cursor_place == GDScriptTokenizer::CURSOR_MIDDLE;
		ExpressionNode *argument = parse_expression(false);
		if (argument == nullptr) {