Merge branch 'ps/ci-gitlab-prepare-for-macos-14-deprecation'

Move gitlab CI from macOS 14 images that are being deprecated. * ps/ci-gitlab-prepare-for-macos-14-deprecation: gitlab-ci: update to macOS 15 images meson: detect broken iconv that requires ICONV_RESTART_RESET meson: simplify iconv-emits-BOM check