Update our testing to support ubuntu-latest containers

[stefanbucur]

No description provided.

[attilaolah]

Looks like Actions have started failing (at least for me) when running under ubuntu-18 containers. It would be nice to support ubuntu-22, although there don't seem to be pre-built binaries for recent Clang versions. (Maybe building clang from source during testing would be simpler at some point.)

That said, the latest main branch of this repo seems to work with ubuntu-22.04. I installed the following dependencies:

apt-get --yes install python-is-python3 python3-distutils pypy-enum34 libtinfo5

Note that libtinfo5 is only needed if the pre-built Clang 16 binary is used, since it is linked against an older version of tinfo.