### 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
assignment->assignee = p_previous_operand;
	assignment->assigned_value = parse_expression(false);
	if (assignment->assigned_value == nullptr) {
		push_error(R"(Expected an expression after "=".)");
	}
	complete_extents(assignment);
#ifdef DEBUG_ENABLED
	if (source_variable != nullptr) {
		if (has_operator && source_variable->assignments == 0) {
			push_warning(assignment, GDScriptWarning::UNASSIGNED_VARIABLE_OP_ASSIGN, source_variable->identifier->name);
		}
		source_variable->assignments += 1;
	}
#endif
	return assignment;
}
GDScriptParser::ExpressionNode *GDScriptParser::parse_await(ExpressionNode *p_previous_operand, bool p_can_assign) {
	AwaitNode *await = alloc_node<AwaitNode>();
	ExpressionNode *element = parse_precedence(PREC_AWAIT, false);
	if (element == nullptr) {
		push_error(R"(Expected signal or coroutine after "await".)");
	}
	await->to_await = element;
	complete_extents(await);
	if (current_function) { 
		current_function->is_coroutine = true;
	}
	return await;
}
GDScriptParser::ExpressionNode *GDScriptParser::parse_array(ExpressionNode *p_previous_operand, bool p_can_assign) {