### 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
break;
			case GDScriptTokenizer::Token::LITERAL:
				if (current.literal.get_type() == Variant::STRING) {
					
					advance();
					if (!match(GDScriptTokenizer::Token::NEWLINE)) {
						push_error("Expected newline after comment string.");
					}
					break;
				}
				[[fallthrough]];
			default:
				
				make_completion_context(COMPLETION_IDENTIFIER, nullptr);
				push_error(vformat(R"(Unexpected "%s" in class body.)", current.get_name()));
				advance();
				break;
		}
		if (token.type != GDScriptTokenizer::Token::STATIC) {
			next_is_static = false;
		}
		if (panic_mode) {
			synchronize();
		}
		if (!p_is_multiline) {
			class_end = true;
		}
	}
}
GDScriptParser::VariableNode *GDScriptParser::parse_variable(bool p_is_static) {