add workaround for 404 error when installing packages in CI workflow for testing Apptainer integration

[boegel]

Fix for failing CI when trying to install dnf package:

Err:19 mirror+file:/etc/apt/apt-mirrors.txt jammy-updates/main amd64 libunbound8 amd64 1.13.1-1ubuntu5.3
  404  Not Found [IP: 52.252.75.106 80]
Ign:20 http://security.ubuntu.com/ubuntu jammy-updates/universe amd64 python3-unbound amd64 1.13.1-1ubuntu5.3
Err:20 mirror+file:/etc/apt/apt-mirrors.txt jammy-updates/universe amd64 python3-unbound amd64 1.13.1-1ubuntu5.3
  404  Not Found [IP: 52.252.75.106 80]
E: Failed to fetch mirror+file:/etc/apt/apt-mirrors.txt/pool/main/u/unbound/libunbound8_1.13.1-1ubuntu5.3_amd64.deb  404  Not Found [IP: 52.252.75.106 80]
Fetched 3190 kB in 1s (3669 kB/s)
E: Failed to fetch mirror+file:/etc/apt/apt-mirrors.txt/pool/universe/u/unbound/python3-unbound_1.13.1-1ubuntu5.3_amd64.deb  404  Not Found [IP: 52.252.75.106 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
Error: Process completed with exit code 100.

We're already using this same workaround in the workflow for testing Singularity integration (see also #4176)

[Micket]

lgtm

change needed