CI Pipeline failure because of apt-get update error

GitLab CI/CD
#1

My CI script keeps failing with the following error. It used to work a couple of weeks ago.

Relevant parts of my CI yaml

image: maven:3.3.9-jdk-8
services:
  - postgres
  - docker:dind

The Error
$ apt-get update -y
Ign http://deb.debian.org jessie InRelease
Get:1 http://deb.debian.org jessie-updates InRelease [7340 B]
Get:2 http://security.debian.org jessie/updates InRelease [44.9 kB]
Ign http://deb.debian.org jessie-backports InRelease
Get:3 http://deb.debian.org jessie Release.gpg [2420 B]
Ign http://deb.debian.org jessie-backports Release.gpg
Get:4 http://deb.debian.org jessie Release [148 kB]
Ign http://deb.debian.org jessie-backports Release
Err http://deb.debian.org jessie-backports/main amd64 Packages

Err http://deb.debian.org jessie-backports/main amd64 Packages
  
Err http://deb.debian.org jessie-backports/main amd64 Packages
  
Err http://deb.debian.org jessie-backports/main amd64 Packages
  
Err http://deb.debian.org jessie-backports/main amd64 Packages
  404  Not Found [IP: 151.101.248.204 80]
Get:5 http://security.debian.org jessie/updates/main amd64 Packages [824 kB]
Get:6 http://deb.debian.org jessie/main amd64 Packages [9098 kB]
Fetched 10.1 MB in 6s (1633 kB/s)
W: Failed to fetch http://deb.debian.org/debian/dists/jessie-updates/InRelease  Unable to find expected entry 'main/binary-amd64/Packages' in Release file (Wrong sources.list entry or malformed file)

W: Failed to fetch http://deb.debian.org/debian/dists/jessie-backports/main/binary-amd64/Packages  404  Not Found [IP: 151.101.248.204 80]

E: Some index files failed to download. They have been ignored, or old ones used instead.
ERROR: Job failed: exit code 1
#2

The jessie-backports and jessie-updates repositories have been removed from all mirrors. See https://lists.debian.org/debian-devel-announce/2019/03/msg00006.html. https://unix.stackexchange.com/questions/508724/failed-to-fetch-jessie-backports-repository describes how to fix it, but the better way is to update your images to stretch. You could use the image maven:3.6.1-jdk-8. To prevent this in the future, you could also just use maven:3-jdk-8