### 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
}
	attribute->base = p_previous_operand;
	if (current.is_node_name()) {
		current.type = GDScriptTokenizer::Token::IDENTIFIER;
	}
	if (!consume(GDScriptTokenizer::Token::IDENTIFIER, R"(Expected identifier after "." for attribute access.)")) {
		complete_extents(attribute);
		return attribute;
	}
	attribute->is_attribute = true;
	attribute->attribute = parse_identifier();
	complete_extents(attribute);
	return attribute;
}
GDScriptParser::ExpressionNode *GDScriptParser::parse_subscript(ExpressionNode *p_previous_operand, bool p_can_assign) {
	SubscriptNode *subscript = alloc_node<SubscriptNode>();
	reset_extents(subscript, p_previous_operand);
	update_extents(subscript);
	make_completion_context(COMPLETION_SUBSCRIPT, subscript);
	subscript->base = p_previous_operand;
	subscript->index = parse_expression(false);
	if (subscript->index == nullptr) {
		push_error(R"(Expected expression after "[".)");
	}
	pop_multiline();
	consume(GDScriptTokenizer::Token::BRACKET_CLOSE, R"(Expected "]" after subscription index.)");
	complete_extents(subscript);
	return subscript;
}
GDScriptParser::ExpressionNode *GDScriptParser::parse_cast(ExpressionNode *p_previous_operand, bool p_can_assign) {