Enable experimental feature for the test fixture
user
```hcl
# Copyright 2022 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

terraform {
  required_version = ">= 1.1.0"

  # TODO: Remove once Terraform 1.3 is released https://github.com/hashicorp/terraform/releases/tag/v1.3.0-alpha20220622
  experiments = [module_variable_optional_attrs]
}
```
assistant