Migrate CI to Ubuntu 24

[goatgoose]

Problem:

Currently, the vast majority of the Codebuild CI jobs use a Ubuntu 18 image:

s2n-tls/codebuild/spec/buildspec_generalbatch.yml

Line 22 in 1ed5624

image: 024603541914.dkr.ecr.us-west-2.amazonaws.com/docker:ubuntu18codebuild

This includes many of the unit test jobs that test combinations of compilers and libcryptos, and the integration test jobs.

In addition to adding a simple unit test job to Ubuntu 24 (#4529), all of the existing unit test combinations and the integration tests should be moved to Ubuntu 24. This will allow newer compiler versions to be more easily tested.

Solution:

Migrate the ubuntu 18 CI image to Ubuntu 24.

[dougch]

As with Arm/nix, tools like sslyze won't be simple to bring forward. Unit test runs should be trivial to get running with minor updates to the install_ubuntu_deps script.