ci: Run tests on llvmpipe from Mesa 24.0.3.

The Mesa version in Debian bookworm (22.3.6) we use for testing is now a bit outdated. While it's valuable to test on older drivers because they might be more representative of what users are running, it's also useful to test on recent drivers, which gives a less noisy signal to developers.

For the moment we enable it only for llvmpipe, because RADV is already passing all the tests anyway. And we don't bother with 32 bit here.

On llvmpipe using Mesa 24 fixes three shader runner tests.