### 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
GDScriptTokenizer::Token::Type op_type = previous.type;
	LiteralNode *constant = alloc_node<LiteralNode>();
	complete_extents(constant);
	switch (op_type) {
		case GDScriptTokenizer::Token::CONST_PI:
			constant->value = Math_PI;
			break;
		case GDScriptTokenizer::Token::CONST_TAU:
			constant->value = Math_TAU;
			break;
		case GDScriptTokenizer::Token::CONST_INF:
			constant->value = INFINITY;
			break;
		case GDScriptTokenizer::Token::CONST_NAN:
			constant->value = NAN;
			break;
		default:
			return nullptr; 
	}
	return constant;
}
GDScriptParser::ExpressionNode *GDScriptParser::parse_unary_operator(ExpressionNode *p_previous_operand, bool p_can_assign) {