olddeps build failing with 404 on packages

[github-actions]

See https://github.com/matrix-org/synapse/actions/runs/5000320207

[DMRobertson]

Various 503s from azure.archive.ubuntu.com.

[clokep]

We've seen this on a bunch of olddeps builds today.

[clokep]

See:

• https://github.com/matrix-org/synapse/actions/runs/5006714379/jobs/8972423986?pr=14678
• https://github.com/matrix-org/synapse/actions/runs/5006329218/jobs/8971540690?pr=15233

   sudo apt-get -qq install build-essential libffi-dev python-dev \
  libxml2-dev libxslt-dev xmlsec1 zlib1g-dev libjpeg-dev libwebp-dev
  shell: /usr/bin/bash -e {0}
  env:
    CARGO_INCREMENTAL: 0
    CARGO_TERM_COLOR: always
    CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
    CACHE_ON_FAILURE: false
E: Failed to fetch http://azure.archive.ubuntu.com/ubuntu/pool/main/libw/libwebp/libwebpdemux2_0.6.1-2ubuntu0.20.04.1_amd64.deb  404  Not Found [IP: 40.119.46.219 80]
E: Failed to fetch http://azure.archive.ubuntu.com/ubuntu/pool/main/libw/libwebp/libwebp-dev_0.6.1-2ubuntu0.20.04.1_amd64.deb  404  Not Found [IP: 40.119.46.219 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

[clokep]

@squahtx suggested:

trial-olddeps does seem broken. I think we either need to apt update manually in the workflow or wait til GitHub update the 20.04 image