google-cloud-platform - Deployment Manager: 別の操作が既に進行中であったため、操作が失敗しました

Question

1 つの cloudsql インスタンスに 2 つのデータベースを作成したいと考えています。ただし、次のように記述するとエラーになります。

resources:
- name: test-instance
  type: sqladmin.v1beta4.instance
  properties:
    region: us-central
    backendType: SECOND_GEN
    instanceType: CLOUD_SQL_INSTANCE
    settings:
      tier: db-f1-micro
- name: test_db1
  type: sqladmin.v1beta4.database
  properties:
    instance: $(ref.test-instance.name)
    charset: utf8mb4
    collation: utf8mb4_general_ci
- name: test_db2
  type: sqladmin.v1beta4.database
  properties
    instance: $(ref.test-instance.name)
    charset: utf8mb4
    collation: utf8mb4_general_ci

出力：

ERROR: (gcloud.deployment-manager.deployments.create) Error in Operation 
[operation-********]
- code: RESOURCE_ERROR
  location: /deployments/sample-deploy/resources/test_db2
   message:
'{"ResourceType":"sqladmin.v1beta4.database","ResourceErrorCode":"403","ResourceErrorMessage":{"code":403,"errors":[{"domain":"global","message":"Operation
    failed because another operation was already in progress.","reason":"operationInProgress"}],"message":"Operation
    failed because another operation was already in progress.","statusMessage":"Forbidden","requestPath":"https://www.googleapis.com/sql/v1beta4/projects/****/instances/test-instance/databases","httpMethod":"POST"}}'

エラーを解決するために何をすべきか教えてください。