### 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;
	UnaryOpNode *operation = alloc_node<UnaryOpNode>();
	switch (op_type) {
		case GDScriptTokenizer::Token::MINUS:
			operation->operation = UnaryOpNode::OP_NEGATIVE;
			operation->variant_op = Variant::OP_NEGATE;
			operation->operand = parse_precedence(PREC_SIGN, false);
			if (operation->operand == nullptr) {
				push_error(R"(Expected expression after "-" operator.)");
			}
			break;
		case GDScriptTokenizer::Token::PLUS:
			operation->operation = UnaryOpNode::OP_POSITIVE;
			operation->variant_op = Variant::OP_POSITIVE;
			operation->operand = parse_precedence(PREC_SIGN, false);
			if (operation->operand == nullptr) {
				push_error(R"(Expected expression after "+" operator.)");
			}
			break;
		case GDScriptTokenizer::Token::TILDE:
			operation->operation = UnaryOpNode::OP_COMPLEMENT;
			operation->variant_op = Variant::OP_BIT_NEGATE;
			operation->operand = parse_precedence(PREC_BIT_NOT, false);
			if (operation->operand == nullptr) {
				push_error(R"(Expected expression after "~" operator.)");
			}
			break;