### 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
PreloadNode *preload = alloc_node<PreloadNode>();
	preload->resolved_path = "<missing path>";
	push_multiline(true);
	consume(GDScriptTokenizer::Token::PARENTHESIS_OPEN, R"(Expected "(" after "preload".)");
	make_completion_context(COMPLETION_RESOURCE_PATH, preload);
	push_completion_call(preload);
	preload->path = parse_expression(false);
	if (preload->path == nullptr) {
		push_error(R"(Expected resource path after "(".)");
	}
	pop_completion_call();
	pop_multiline();
	consume(GDScriptTokenizer::Token::PARENTHESIS_CLOSE, R"*(Expected ")" after preload path.)*");
	complete_extents(preload);
	return preload;
}
GDScriptParser::ExpressionNode *GDScriptParser::parse_lambda(ExpressionNode *p_previous_operand, bool p_can_assign) {
	LambdaNode *lambda = alloc_node<LambdaNode>();
	lambda->parent_function = current_function;
	FunctionNode *function = alloc_node<FunctionNode>();
	function->source_lambda = lambda;
	function->is_static = current_function != nullptr ? current_function->is_static : false;
	if (match(GDScriptTokenizer::Token::IDENTIFIER)) {
		function->identifier = parse_identifier();
	}
	bool multiline_context = multiline_stack.back()->get();
	
	push_multiline(false);
	if (multiline_context) {
		tokenizer.push_expression_indented_block();