[SPIRV][Vulkan] OpCapability Kernel being set on Shaders

[llvm-beanz]

I'm seeing a few cases where Shaders are being generated with OpCapability Kernel applied in addition to OpCapability Shader. Seems like those two should be mutually exclusive.

Reproduction links:

• https://godbolt.org/z/Mx8Ef17e5
• https://godbolt.org/z/3Ez1eY1qj
• https://godbolt.org/z/6EY9EaPGv