Update to CLang 18

[marosset]

The common ci-workflow-setup workflow installs CLang17 on Ubuntu and Mariner Linux.
We should upgrade to CLang 18 everywhere for consistency.

[marosset]

Ubuntu runners have been updated to use clang 18 toolchain.
The AzLinux 3 runners are using clang 18 link

Unfortunately there aren't easily consumable clang18 packages for mariner linux and we're eventually going to faze that disto out in favor of AzLinux 3 so I think we can close this issue.