Json 将react应用程序推送到heroku时，纱线不断重复

当我尝试将react应用程序推送到Heroku时，它运行的是“纱线”，但下面这句话一直在重复

$ cd ./frontend && yarn
remote:        yarn install v1.22.10
remote:        [1/4] Resolving packages...
remote:        success Already up-to-date.
remote:        $ cd ./frontend && yarn
remote:        yarn install v1.22.10
remote:        [1/4] Resolving packages...
remote:        success Already up-to-date.
remote:        $ cd ./frontend && yarn
remote:        yarn install v1.22.10
remote:        [1/4] Resolving packages...
remote:        success Already up-to-date.

我有一个server.js，它在express上运行，但我认为这不是问题所在。 React之外的package.json中的步骤是：

{
  "name": "aras",
  "version": "1.0.0",
  "description": "mafia video game",
  "main": "index.js",
  "license": "MIT",
  "scripts": {
    "start": "PROD=true node server.js",
    "postinstall": "cd ./frontend && yarn"
  },
  "dependencies": {
    "dotenv": "^8.2.0",
    "express": "^4.17.1",
    "socket.io": "^4.0.1",
    "uuid": "^8.3.2"
  }
}

当我将cd放入react应用程序时，package.json中的步骤如下：

"scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject",
    "postinstall": "yarn build"
  },

我曾尝试删除纱线和节点模块，并再次安装它们，但没有任何效果。 注意：前端目录是我的react应用程序，server.js是express