### Godot version

any version after 74458b6

### System information

Linux x64, but likely irrelevant

### Issue description

OpenXR action maps are not properly exported in recent builds of Godot 4: the `.res` file is small and does no longer seem to contain anything of use. In-game, no actions are passed on to OpenXR (obviously).

I bisected the issue down to https://github.com/godotengine/godot/commit/74458b6e9bed0f28db3374c7406eacbcf4b09b9d, which was merged in #70377.

### Steps to reproduce

1. Delete any previous export files (`.godot/exported/*/*.pkg`)
2. Perform an export (I did one for Android, but it likely works with anything)
3. Observe OpenXR actions not working in the export (error spam 'sync_action_sets: Condition "active_sets.size() == 0"'), and the exported action map file being very small (`.godot/exported/*/*.pkg`, from a few tens of kilobytes down to 296 bytes)

### Minimal reproduction project

Any OpenXR project can be used, such as https://github.com/BastiaanOlij/godot4_openxr_demo
if (fec.source_md5 == md5) {
				
				fec.source_modified_time = mod_time;
				fec.used = true;
				return fec.saved_path.is_empty() ? p_path : fec.saved_path;
			}
		}
	}
	FileExportCache fec;
	fec.used = true;
	fec.source_modified_time = FileAccess::get_modified_time(p_path);
	String md5 = FileAccess::get_md5(p_path);
	if (FileAccess::exists(p_path + ".import")) {
		
		md5 += FileAccess::get_md5(p_path + ".import");
	}
	fec.source_md5 = md5;
	
	String type = ResourceLoader::get_resource_type(p_path);
	bool modified = false;
	String save_path;
	if (type == "PackedScene") { 
		Ref<PackedScene> ps = ResourceLoader::load(p_path, "PackedScene", ResourceFormatLoader::CACHE_MODE_IGNORE);
		ERR_FAIL_COND_V(ps.is_null(), p_path);
		Node *node = ps->instantiate(PackedScene::GEN_EDIT_STATE_INSTANCE); 
		ERR_FAIL_COND_V(node == nullptr, p_path);
		if (!customize_scenes_plugins.is_empty()) {
			for (Ref<EditorExportPlugin> &plugin : customize_scenes_plugins) {
				Node *customized = plugin->_customize_scene(node, p_path);
				if (customized != nullptr) {