### 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
bool changed = false;
	List<Variant> keys;
	dict.get_key_list(&keys);
	for (const Variant &K : keys) {
		Variant v = dict[K];
		switch (v.get_type()) {
			case Variant::OBJECT: {
				Ref<Resource> res = v;
				if (res.is_valid()) {
					for (Ref<EditorExportPlugin> &plugin : customize_resources_plugins) {
						Ref<Resource> new_res = plugin->_customize_resource(res, "");
						if (new_res.is_valid()) {
							changed = true;
							if (new_res != res) {
								dict[K] = new_res;
								res = new_res;
							}
							break;
						}
					}
					
					if (res.is_valid() && !res->get_path().is_resource_file() && _export_customize_object(res.ptr(), customize_resources_plugins), true) {
						changed = true;
					}
				}
			} break;
			case Variant::DICTIONARY: {
				Dictionary d = v;