Ubuntu and package installation

[wawrzek]

Details

In the act workflows installing Ubuntu packages with apt, the list of sources has to be refreshed first with apt update. The same is not required in GHA. I can run apt install -y $PACKAGE straight away.
AFAIK that's the 'feature' of docker image, nothing particular to act. I suggest adding one-liner to documentation, something like:
"Ubuntu docker image requires a source list refresh before running apt install. Therefore, any workflow with the deb package installation action requires the apt update to be run first."