### 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
String result;
	int from = 0;
	int buffer_start = 0;
	const int len = line.length();
	bool process = true;
	while (process) {
		switch (r_state) {
			case DOC_LINE_NORMAL: {
				int lb_pos = line.find_char('[', from);
				if (lb_pos < 0) {
					process = false;
					break;
				}
				int rb_pos = line.find_char(']', lb_pos + 1);
				if (rb_pos < 0) {
					process = false;
					break;
				}
				from = rb_pos + 1;
				String tag = line.substr(lb_pos + 1, rb_pos - lb_pos - 1);
				if (tag == "code") {
					r_state = DOC_LINE_IN_CODE;
				} else if (tag == "codeblock") {
					if (lb_pos == 0) {
						line_join = "\n";
					} else {
						result += line.substr(buffer_start, lb_pos - buffer_start) + '\n';
					}
					result += "[codeblock]";
					if (from < len) {