Upgrade CI images

[mwtoews]

This upgrades the CI ubuntu images from 20.04 to 22.04. Also clang 10 to clang 12, as supported by these images.

[mwtoews]

A few notes:

• clang-11 with ASAN threw many errors, unsure why. These seem to go away with clang-12, which is fine with me, but I have not investigated if the errors from clang-11 are worth looking into.
• There are issues passing (e.g.) CXXFLAGS=-Werror with find_packages(), as this fails finding packages (the warning/error is hidden in a log file). A possible workaround is used for CMake 3.22.1 to remove this flag until after project(), then restored as CMAKE_CXX_FLAGS. This workaround can be removed at a later time to use -D CMAKE_COMPILE_WARNING_AS_ERROR=ON instead, added with CMake 3.24.