### 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
switch (kind) {
		case VARIANT:
			return "Variant";
		case BUILTIN:
			if (builtin_type == Variant::NIL) {
				return "null";
			}
			if (builtin_type == Variant::ARRAY && has_container_element_type()) {
				return vformat("Array[%s]", container_element_type->to_string());
			}
			return Variant::get_type_name(builtin_type);
		case NATIVE:
			if (is_meta_type) {
				return GDScriptNativeClass::get_class_static();
			}
			return native_type.operator String();
		case CLASS: