ci: Validate the SPIR-V code.

In order to validate SPIR-V code we have to fix a little bug that causes us to emit invalid SPIR-V code in some cases. That's technically a bug, so it should be good to fix it in 1.10; unfortunately the way the bug is fixed right now is not ideal, because in some cases it causes many push constants to be wasted, potentially reaching the Vulkan implementation limit, so some application that used to work might stop working. Eventually we should implement a better allocator for push constants, and include an alternative path if the Vulkan implementation doesn't offer enough push constants.