ci: enable clang-15
ci: enable clang-15

Github has officially enabled Ubuntu 22.04 LTS images for ci which
got out-of-the-box gcc-11 and clang-14.

We also drop testing against clang-12 and enable testing against clang-15.

Signed-off-by: Dmitry Rogozhkin <01f0df9cc32cbf6a7f0faa5c8376e6cf28354d70@intel.com>

Intel-Media-SDK/MediaSDK,Intel-Media-SDK/MediaSDK,Intel-Media-SDK/MediaSDK,Intel-Media-SDK/MediaSDK,Intel-Media-SDK/MediaSDK