Merge topic 'ci-import-std-gcc'

7318e9ab1c ci: Remove now-redundant GCC 15 C++ import std jobs
47d8b3c635 ci: Migrate `CMAKE_CXX_STDLIB_MODULES_JSON` job to Fedora base image

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !11845