Ubuntu 22.04/g++11.4/clang 14 becoming minimum tested version

[wsnyder]

In March, Verilator will be disabling the Ubuntu 20.04 runners, in advance of GitHub disabling them temporarily during March 4, 11, 18 & 25, and permanently on April 1st.

This means that all Verilator action testing will occur on Ubuntu 22.04 or newer, meaning compiles will use g++ 11.4, clang 14.0, MSVC++ 19.42, or newer versions of each.

Users are recommended to use Ubuntu 22.04/g++ 11.4/clang 14 or newer for the best experiences, otherwise (e.g. if using RedHat 8) you will likely need to repair any compiler fallout and/or patch sources as the code evolves to use c++ supported by only those compiler versions noted above or newer.