### 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 (f.is_valid()) {
			String l = f->get_line();
			while (l != String()) {
				Vector<String> fields = l.split("::");
				if (fields.size() == 4) {
					FileExportCache fec;
					String path = fields[0];
					fec.source_md5 = fields[1].strip_edges();
					fec.source_modified_time = fields[2].strip_edges().to_int();
					fec.saved_path = fields[3];
					fec.used = false; 
					export_cache[path] = fec;
				}
				l = f->get_line();
			}
		} else {
			
			Ref<DirAccess> d = DirAccess::create(DirAccess::ACCESS_RESOURCES);
			d->change_dir(ProjectSettings::get_singleton()->get_project_data_path());
			d->make_dir_recursive("exported/" + itos(custom_resources_hash));
		}
	}
	
	int idx = 0;
	int total = paths.size();
	for (const String &E : paths) {
		String path = E;
		String type = ResourceLoader::get_resource_type(path);
		if (FileAccess::exists(path + ".import")) {