Fix CI: add sudo apt-get update to actions

[mikekryjak]

CI is failing here, and presumably also in other PRs that have had test actions since:
#336

The error is:

Ign:4 https://security.ubuntu.com/ubuntu noble-updates/main amd64 libcurl4-openssl-dev amd64 8.5.0-2ubuntu10.7
Err:4 mirror+file:/etc/apt/apt-mirrors.txt noble-updates/main amd64 libcurl4-openssl-dev amd64 8.5.0-2ubuntu10.7
  404  Not Found [IP: 52.161.185.214 80]
E: Failed to fetch mirror+file:/etc/apt/apt-mirrors.txt/pool/main/c/curl/libcurl4-openssl-dev_8.5.0-2ubuntu10.7_amd64.deb  404  Not Found [IP: 52.161.185.214 80]
Fetched 4720 kB in 2s (2450 kB/s)
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

I tried to follow the error advice and add sudo apt-get update, which seems to resolve the same issue in xHermes. This PR adds it to xBOUT CI.