### 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
#include "gdscript_parser.h"
#include "gdscript.h"
#ifdef DEBUG_ENABLED
#include "gdscript_warning.h"
#endif
#include "core/config/project_settings.h"
#include "core/io/file_access.h"
#include "core/io/resource_loader.h"
#include "core/math/math_defs.h"
#include "scene/main/multiplayer_api.h"
#ifdef DEBUG_ENABLED
#include "core/os/os.h"
#include "core/string/string_builder.h"
#include "servers/text_server.h"
#endif
#ifdef TOOLS_ENABLED
#include "editor/editor_settings.h"
#endif
static HashMap<StringName, Variant::Type> builtin_types;
Variant::Type GDScriptParser::get_builtin_type(const StringName &p_type) {