如何设置cloud-init的apt模块？

如何解决如何设置cloud-init的apt模块？

我尝试将一个软件包从debian测试库安装到稳定的debian安装中。只有一个包。除非测试版本指定，否则任何测试都不应安装！

我的apt cloud-init模块出错：

Cloud-init v. 20.2 running 'modules:config' at Wed,07 Oct 2020 10:17:21 +0000. Up 1.88 seconds.
2020-10-07 10:17:21,487 - util.py[WARNING]: Running module apt-configure (<module 'cloudinit.config.cc_apt_configure' from '/usr/lib/python3/dist-packages/cloudinit/config/cc_apt_configure.py'>) failed

cloud-init文件为：

#cloud-config
timezone: Europe/Paris
hostname: ansible-master
users:
  - name: myuser
    sudo: ['ALL=(ALL) NOPASSWD:ALL']
    groups: sudo
    shell: /bin/bash
    ssh_authorized_keys:
      - ssh-ed25519 AAAAC3NzaC1lZSI1NTE5AAAAIBD9IUXIhtKcNtwLUPjSkQhHhRd0SowyMF3IFCZbCOl3
chpasswd:
  list: |
    root:tempPass
    myuser:temp
apt:
  preserve_sources_list: false
  primary:
    - arches: [amd64,i386,default]
      uri: http://deb.debian.org/debian
  security:
    - uri: http://security.debian.org/debian-security
  sources_list: | # Written by cloud-init custom template
    deb $MIRROR $RELEASE main
    deb $SECURITY $RELEASE/updates main
    deb $MIRROR $RELEASE-updates main
    deb $MIRROR bullseye main
  conf: | #APT config by cloud-init
    APT {
      Get {
        Default-Release "buster";
        Assume-Yes "true";
        Fix-Broken "true";
      };
    };
packages:
  - [openssh-client,8.3p1-1_amd64]
  - [openssh-server,8.3p1-1_amd64]
package_update: false
package_upgrade: false
final_message: "The system is finally up,after $UPTIME seconds"

我为apt conf尝试了其他语法，例如波纹管，但对我没有任何帮助...

conf: | #APT config by cloud-init
  APT {
    Default-Release "buster";
    Get {
      Assume-Yes "true";
      Fix-Broken "true";
    };
  };

如果有人有这样做的想法。预先感谢