### Godot version

4.0 -> latest

**I've tested all this versions:**
4.0, 4.0.1, 4.0.2, 4.0.3, 4.0.4
4.1, 4.1.1
4.2 dev 4

in all this versions problem exists.

### System information

Fedora 38, macOS

### Issue description

I have found a very strange bug while generating translations. The presence of a method modifying the dictionary's content causes the editor to crash during the generation of the translation template.

The mere presence of an uninvoked method causes a crash.

**Edit: The issue occurs not only with singletons. Any script containing a method that modifies any dictionary leads to a crash.**

### Steps to reproduce

**Project -> Project Settings -> Localizations -> Generate POT -> Add (Add your singleton)**

```
extends Node

var session_data = {
	"coins" : 0,
	"power": 0
}

var shop_items = [
	{
		"id": "max_hp",
		"name": tr("First Shop Item"),
		"desc": tr("Great tool."),
	}
]

func add_power(val: int):
	session_data["power"] += val
```

_⚠️ Problem is in add_power method, not in shop_items._


**Project -> Project Settings -> Localizations -> Generate POT -> Generate**

And... Crash.


[Nagranie ekranu z 2023-09-14 13-10-42.webm](https://github.com/godotengine/godot/assets/5132385/6a00805a-34c8-408e-9b00-eb5875301312)



### Minimal reproduction project

[translation_gm_crash.zip](https://github.com/godotengine/godot/files/12104763/translation_gm_crash.zip)

_Just open project and go to: Project -> Project Settings -> Localizations -> Generate POT -> Generate_

ERR_FAIL_NULL_V(p_expression, false);
	return p_expression->is_constant && (p_expression->reduced_value.get_type() == Variant::STRING || p_expression->reduced_value.get_type() == Variant::STRING_NAME);
}
void GDScriptEditorTranslationParserPlugin::_traverse_class(const GDScriptParser::ClassNode *p_class) {
	for (int i = 0; i < p_class->members.size(); i++) {
		const GDScriptParser::ClassNode::Member &m = p_class->members[i];
		
		switch (m.type) {
			case GDScriptParser::ClassNode::Member::CLASS:
				_traverse_class(m.m_class);
				break;
			case GDScriptParser::ClassNode::Member::FUNCTION:
				_traverse_function(m.function);
				break;
			case GDScriptParser::ClassNode::Member::VARIABLE:
				_read_variable(m.variable);
				break;
			default:
				break;
		}
	}
}
void GDScriptEditorTranslationParserPlugin::_traverse_function(const GDScriptParser::FunctionNode *p_func) {
	_traverse_block(p_func->body);
}
void GDScriptEditorTranslationParserPlugin::_read_variable(const GDScriptParser::VariableNode *p_var) {