apt-get update Fails

this is the resulting error
`W: There is no public key available for the following key IDs:
9D6D8F6BC857C906`

```Removing intermediate container 479c0d086d3b

Step 2/16 : RUN apt-get update && apt-get install -y --no-install-recommends build-essential gettext git libffi-dev libjpeg-dev libmemcached-dev libpq-dev libssl-dev libxml2-dev libxslt1-dev locales nginx python-dev python-virtualenv python3-dev sudo supervisor zlib1g-dev && apt-get clean && rm -rf /var/lib/apt/lists/* && dpkg-reconfigure locales && locale-gen C.UTF-8 && /usr/sbin/update-locale LANG=C.UTF-8 && mkdir /etc/pretix && mkdir /data && useradd -ms /bin/bash -d /pretix -u 15371 pretixuser && echo 'pretixuser ALL=(ALL) NOPASSWD: /usr/bin/supervisord' >> /etc/sudoers && mkdir /static

---> Running in ce9daa6fe1d6

Get:1 http://security.debian.org jessie/updates InRelease [44.9 kB]

Ign http://http.debian.net jessie InRelease

Ign http://http.debian.net jessie-updates InRelease

Get:2 http://http.debian.net jessie Release.gpg [2420 B]

Ign http://http.debian.net jessie-updates Release.gpg

Get:3 http://http.debian.net jessie Release [148 kB]

Ign http://http.debian.net jessie-updates Release

Get:4 http://security.debian.org jessie/updates/main amd64 Packages [825 kB]

Get:5 http://http.debian.net jessie/main amd64 Packages [9098 kB]

Err http://http.debian.net jessie-updates/main amd64 Packages

Err http://http.debian.net jessie-updates/main amd64 Packages

Err http://http.debian.net jessie-updates/main amd64 Packages

Err http://http.debian.net jessie-updates/main amd64 Packages
404 Not Found

Fetched 10.1 MB in 8s (1190 kB/s)

W: There is no public key available for the following key IDs:
9D6D8F6BC857C906
W: Failed to fetch http://http.debian.net/debian/dists/jessie-updates/main/binary-amd64/Packages 404 Not Found

E: Some index files failed to download. They have been ignored, or old ones used instead.```

Bắt đầu bằng cách xác định Dockerfile chứa lệnh Step 2/16 RUN apt-get update được hiển thị và kiểm tra các nguồn gói Debian jessie của nó. Tái hiện quá trình build image, sau đó xác minh rằng apt-get update và việc cài đặt các gói được liệt kê hoàn tất mà không có lỗi thiếu khóa hoặc lỗi 404.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.