Failed CI/Syntax

[jeisenbe]

See https://github.com/gravitystorm/openstreetmap-carto/actions/runs/99555421

Set up xmllint 4s
  Run sudo apt-get install -qq --no-install-recommends libxml2-utils
  E: Failed to fetch http://ppa.launchpad.net/ondrej/php/ubuntu/pool/main/libx/libxml2/libxml2-    utils_2.9.10+dfsg-2+ubuntu18.04.1+deb.sury.org+1_amd64.deb  404  Not Found [IP: 91.189.95.83 80]
  E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
##[error]Process completed with exit code 100.

This did not affect the rendering, and I don't see any changes in the code that could have caused this. Is there some problem with the linked server at ppa.launchpad.net perhaps?

[StyXman]

There is a new version, its trying to install +1 and available is +3. I wonder two things:

• Maybe apt update should be run prior to package installation.
• Why are we using an external ppa for libxml? The one in the distro (I assume Ubuntu) is not enough?

[pnorman]

• Why are we using an external ppa for libxml? The one in the distro (I assume Ubuntu) is not enough?

We're not specifying an external PPA, that seems to be coming from https://github.com/actions/virtual-environments/blob/ubuntu18/20200430.1/images/linux/Ubuntu1804-README.md