### 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 (!p_can_assign) {
		push_error("Assignment is not allowed inside an expression.");
		return parse_expression(false); 
	}
	if (p_previous_operand == nullptr) {
		return parse_expression(false); 
	}
#ifdef DEBUG_ENABLED
	VariableNode *source_variable = nullptr;
#endif
	switch (p_previous_operand->type) {
		case Node::IDENTIFIER: {
#ifdef DEBUG_ENABLED