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

These Clang 19-identified issues need to be addressed first:

• !9313 (merged)
• !9317 (merged)
• !9316 (merged)
• !9315 (merged)

Validation pipelines for backports:

• v9.21 - https://gitlab.isc.org/isc-projects/bind9/-/pipelines/191211
• v9.20 - https://gitlab.isc.org/isc-projects/bind9/-/pipelines/191512
• v9.18 - https://gitlab.isc.org/isc-projects/bind9/-/pipelines/191904

Prereq: isc-projects/images!328

Backport of MR !9296 (merged)