### 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
DictionaryNode *dictionary = alloc_node<DictionaryNode>();
	bool decided_style = false;
	if (!check(GDScriptTokenizer::Token::BRACE_CLOSE)) {
		do {
			if (check(GDScriptTokenizer::Token::BRACE_CLOSE)) {
				
				break;
			}
			
			ExpressionNode *key = parse_expression(false, true); 
			if (key == nullptr) {
				push_error(R"(Expected expression as dictionary key.)");
			}
			if (!decided_style) {
				switch (current.type) {
					case GDScriptTokenizer::Token::COLON:
						dictionary->style = DictionaryNode::PYTHON_DICT;
						break;
					case GDScriptTokenizer::Token::EQUAL:
						dictionary->style = DictionaryNode::LUA_TABLE;
						break;
					default:
						push_error(R"(Expected ":" or "=" after dictionary key.)");