### 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
case GDScriptTokenizer::Token::BREAKPOINT:
			advance();
			result = alloc_node<BreakpointNode>();
			complete_extents(result);
			end_statement(R"("breakpoint")");
			break;
		case GDScriptTokenizer::Token::ASSERT:
			advance();
			result = parse_assert();
			break;
		case GDScriptTokenizer::Token::ANNOTATION: {
			advance();
			is_annotation = true;
			AnnotationNode *annotation = parse_annotation(AnnotationInfo::STATEMENT);
			if (annotation != nullptr) {
				annotation_stack.push_back(annotation);
			}
			break;
		}
		default: {
			
			ExpressionNode *expression = parse_expression(true); 
			bool has_ended_lambda = false;
			if (expression == nullptr) {
				if (in_lambda) {
					
					lambda_ended = true;
					has_ended_lambda = true;
				} else {
					advance();