无法使用Php 7.3将laravel 7部署到Google Cloud Platform

我无法使用Php 7.3在GCP上部署新的Laravel安装。在php 7.2（runtime: php72）上可以使用，但是我不能在GCP中使用工匠，因为composer install即使我的嘲笑是，作曲家也不允许我安装（）导致此错误"mockery/mockery": "1.3.1"：

mockery/mockery 1.4.1 requires php ^7.3 || ^8.0 -> your PHP version (7.2.32) does not satisfy that requirement

我当前在本地计算机上使用的PHP版本是：PHP 7.3.20。

我的app.yaml文件：

runtime: php73
env: flex

runtime_config:
  document_root: public

# Ensure we skip ".env", which is only for local development
skip_files:
  - .env

env_variables:
  # Put production environment variables here.
  APP_LOG: errorlog
  APP_KEY: base64:JTS6tuNNbTilw0275mq7hQe6DN7wrlLZPD8W0bELZHk=

beta_settings:
  cloud_sql_instances: xxxx

我的composer.json文件是：

{
    "name": "laravel/laravel",
    "type": "project",
    "description": "The Laravel Framework.",
    "keywords": [
        "framework",
        "laravel"
    ],
    "license": "MIT",
    "require": {
        "php": "^7.3",
        "fideloper/proxy": "^4.2",
        "fruitcake/laravel-cors": "^1.0",
        "guzzlehttp/guzzle": "^6.3",
        "laravel/framework": "^7.0",
        "laravel/tinker": "^2.0",
        "laravel/ui": "^2.1",
        "pusher/pusher-php-server": "^4.1"
    },
    "require-dev": {
        "fzaninotto/faker": "^1.9.1",
        "mockery/mockery": "^1.4.0",
        "nunomaduro/collision": "^4.1",
        "phpunit/phpunit": "^8.5"
    },
    "config": {
        "optimize-autoloader": true,
        "preferred-install": "dist",
        "sort-packages": true
    },
    "extra": {
        "laravel": {
            "dont-discover": []
        }
    },
    "autoload": {
        "psr-4": {
            "App\\": "app/"
        },
        "classmap": [
            "database/seeds",
            "database/factories"
        ]
    },
    "autoload-dev": {
        "psr-4": {
            "Tests\\": "tests/"
        }
    },
    "minimum-stability": "dev",
    "prefer-stable": true,
    "scripts": {
        "post-autoload-dump": [
            "Illuminate\\Foundation\\ComposerScripts::postAutoloadDump",
            "@php artisan package:discover --ansi"
        ],
        "post-root-package-install": [
            "@php -r \"file_exists('.env') || copy('.env.example', '.env');\""
        ],
        "post-create-project-cmd": [
            "@php artisan key:generate --ansi"
        ], 
        "post-install-cmd": [
            "chmod -R 755 bootstrap\/cache",
            "php artisan cache:clear"
        ]
    }
}

我尝试从composer.json更改版本以匹配php 7.3，但没有成功。