### 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 op = previous;
	BinaryOpNode *operation = alloc_node<BinaryOpNode>();
	reset_extents(operation, p_previous_operand);
	update_extents(operation);
	Precedence precedence = (Precedence)(get_rule(op.type)->precedence + 1);
	operation->left_operand = p_previous_operand;
	operation->right_operand = parse_precedence(precedence, false);
	complete_extents(operation);
	if (operation->right_operand == nullptr) {
		push_error(vformat(R"(Expected expression after "%s" operator.")", op.get_name()));
	}
	
	switch (op.type) {
		case GDScriptTokenizer::Token::PLUS:
			operation->operation = BinaryOpNode::OP_ADDITION;
			operation->variant_op = Variant::OP_ADD;
			break;
		case GDScriptTokenizer::Token::MINUS:
			operation->operation = BinaryOpNode::OP_SUBTRACTION;
			operation->variant_op = Variant::OP_SUBTRACT;
			break;
		case GDScriptTokenizer::Token::STAR:
			operation->operation = BinaryOpNode::OP_MULTIPLICATION;
			operation->variant_op = Variant::OP_MULTIPLY;
			break;
		case GDScriptTokenizer::Token::SLASH:
			operation->operation = BinaryOpNode::OP_DIVISION;
			operation->variant_op = Variant::OP_DIVIDE;
			break;