### 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
} else if (head->has_member(first)) {
		class_names = p_qualified_name.split("::");
		GDScriptParser::ClassNode::Member member = head->get_member(first);
		if (member.type == GDScriptParser::ClassNode::Member::CLASS) {
			result = member.m_class;
		}
	}
	
	for (int i = 1; result != nullptr && i < class_names.size(); i++) {
		String current_name = class_names[i];
		GDScriptParser::ClassNode *next = nullptr;
		if (result->has_member(current_name)) {
			GDScriptParser::ClassNode::Member member = result->get_member(current_name);
			if (member.type == GDScriptParser::ClassNode::Member::CLASS) {
				next = member.m_class;
			}
		}
		result = next;
	}
	return result;
}
bool GDScriptParser::has_class(const GDScriptParser::ClassNode *p_class) const {
	if (head->fqcn.is_empty() && p_class->fqcn.get_slice("::", 0).is_empty()) {
		return p_class == head;
	} else if (p_class->fqcn.begins_with(head->fqcn)) {
		return find_class(p_class->fqcn.trim_prefix(head->fqcn)) == p_class;
	}
	return false;
}
GDScriptParser::ClassNode *GDScriptParser::parse_class(bool p_is_static) {