Test compatibility with SingularityCE 4.x series

[tsibley]

Two parts to this:

1. Support using the 4.x series in CI, related to dev: Test against the SingularityCE 3.x series in CI #314. It should be straightforward to fix the installation issues by installing the new deps ahead of time. For reference, the DEBIAN/control files of the latest 3.x vs. 4.x releases diff as:

    Package: singularity-ce
   -Version: 3.11.5-jammy
   +Version: 4.0.0-jammy
    Architecture: amd64
    Maintainer: Sylabs Community Packaging <community@sylabs.io>
   -Installed-Size: 133061
   -Depends: libc6 (>= 2.34), libglib2.0-0 (>= 2.35.8), libseccomp2 (>= 2.5.0), crun | runc, cryptsetup-bin, squashfs-tools, uidmap
   -Conflicts: apptainer, singularity-container, singularitypro24, singularitypro25, singularitypro26, singularitypro31, singularitypro35, singularitypro37, singularitypro39
   +Installed-Size: 132090
   +Depends: libc6 (>= 2.34), libfuse2 (>= 2.6), libglib2.0-0 (>= 2.35.8), libseccomp2 (>= 2.5.0), zlib1g (>= 1:1.1.4), crun (>= 1.5.0) | runc, cryptsetup-bin, fuse, squashfs-tools, uidmap
   +Recommends: squashfs-tools-ng
   +Conflicts: apptainer, singularity-container, singularitypro24, singularitypro25, singularitypro26, singularitypro31, singularitypro311, singularitypro35, singularitypro37, singularitypro39
    Section: admin
    Priority: optional
    Homepage: https://sylabs.io/singularity

2. Test that our Singularity runner/runtime still works with 4.x, beyond what's tested by CI. Run it thrus its paces a bit manually and look for oddities.