### 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
return static_cast<LiteralNode *>(parse_literal(nullptr, false));
}
GDScriptParser::ExpressionNode *GDScriptParser::parse_literal(ExpressionNode *p_previous_operand, bool p_can_assign) {
	if (previous.type != GDScriptTokenizer::Token::LITERAL) {
		push_error("Parser bug: parsing literal node without literal token.");
		ERR_FAIL_V_MSG(nullptr, "Parser bug: parsing literal node without literal token.");
	}
	LiteralNode *literal = alloc_node<LiteralNode>();
	complete_extents(literal);
	literal->value = previous.literal;
	return literal;
}
GDScriptParser::ExpressionNode *GDScriptParser::parse_self(ExpressionNode *p_previous_operand, bool p_can_assign) {
	if (current_function && current_function->is_static) {
		push_error(R"(Cannot use "self" inside a static function.)");
	}
	SelfNode *self = alloc_node<SelfNode>();
	complete_extents(self);
	self->current_class = current_class;
	return self;
}
GDScriptParser::ExpressionNode *GDScriptParser::parse_builtin_constant(ExpressionNode *p_previous_operand, bool p_can_assign) {