Be compatible with gcc 14. (Closes: #1086208) and import NMUs

(This branch imports the three missing NMUs by merging with current sid as one commit. If you have a better way to do that, feel free to do so then cherry-pick my actual bug fix.)

This is because Vulkan handles are always 64-bit, even when pointers aren't: https://sources.debian.org/src/vulkan-loader/1.3.296.0-1/vulkan-headers/include/vulkan/vulkan_core.h/#L29

Hence, the fix is to use VK_NULL_HANDLE not plain NULL.

Upstream appear to have the same issue (though I haven't actually tested this).

This also adds a salsa-ci.yml file, but if you want to actually use it you'll need to point Settings (in the Salsa web interface) > CI/CD > General pipelines > CI/CD configuration file there. (It currently points to the upstream CI, which doesn't work here.) The lintian and blhc failures are probably pre-existing real issues, but sufficiently minor ones that they don't have to be dealt with right now.