Update to build on Ubuntu Noble

[Baltoli]

This PR sets up a parallel build for Ubuntu 24.04 (Noble) alongside our current 22.04 (Jammy) build. Everywhere where we previously built only on Jammy, we now build on both:

• Testing build-from-source on PRs
• Testing Ubuntu .deb package creation on PRs
• Releasing .deb packages on release

The changes here are largely procedural; there are only a couple of places we need to do things that aren't just pattern-matching or version parameterisation:

• Use the modern pipx tool to install lit
• Bump the version of pybind we use to be compatible with the one used in Noble (the one we had previously was backwards- but not forwards-compatible).

On Noble, we use LLVM 17 for the time being because of a known bug affecting LLVM 18 in the package repositories that prevents us from using it to package .debs. It does not affect source builds in the same way; there's no real downside to doing this other than not having a totally up-to-date LLVM dependency.

[Baltoli]

Note that this PR will look like checks are missing; this is because of the matrix renaming. I'll update the branch protection rules when the PR is ready to merge.