### 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
if (!for_completion) {
		return;
	}
	CompletionCall call;
	call.call = p_call;
	call.argument = 0;
	completion_call_stack.push_back(call);
	if (previous.cursor_place == GDScriptTokenizer::CURSOR_MIDDLE || previous.cursor_place == GDScriptTokenizer::CURSOR_END || current.cursor_place == GDScriptTokenizer::CURSOR_BEGINNING) {
		completion_call = call;
	}
}
void GDScriptParser::pop_completion_call() {
	if (!for_completion) {
		return;
	}
	ERR_FAIL_COND_MSG(completion_call_stack.is_empty(), "Trying to pop empty completion call stack");
	completion_call_stack.pop_back();
}
void GDScriptParser::set_last_completion_call_arg(int p_argument) {
	if (!for_completion || passed_cursor) {
		return;
	}
	ERR_FAIL_COND_MSG(completion_call_stack.is_empty(), "Trying to set argument on empty completion call stack");
	completion_call_stack.back()->get().argument = p_argument;
}
Error GDScriptParser::parse(const String &p_source_code, const String &p_script_path, bool p_for_completion) {