[9.18] chg: ci: Update Clang to version 19

These Clang 19-identified issues need to be addressed first:
- [x] isc-projects/bind9!9313
- [x] isc-projects/bind9!9317
- [x] isc-projects/bind9!9316
- [x] isc-projects/bind9!9315

Validation pipelines for backports:
- [x] ~"v9.21" - https://gitlab.isc.org/isc-projects/bind9/-/pipelines/191211
- [x] ~"v9.20" - https://gitlab.isc.org/isc-projects/bind9/-/pipelines/191512
- [x] ~"v9.18" - https://gitlab.isc.org/isc-projects/bind9/-/pipelines/191904

Prereq: isc-projects/images!328

Backport of MR !9296

Merge branch 'backport-mnowak/llvm-19-9.18' into 'bind-9.18'

See merge request isc-projects/bind9!9391