[CI] Uses pip's cmake
[CI] Uses pip's cmake

LLVM will soon require a cmake version newer than the one available
through apt. pip's cmake is up to data, currently at version 3.17.
Context: https://github.com/GPUOpen-Drivers/llpc/issues/727#issuecomment-651877672.

GPUOpen-Drivers/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc,googlestadia/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc,googlestadia/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc