build

CI: Replace macos-12 with macos-15 due to deprecation #246

Job	Run time
Upload the source	1m 25s
macos (macos-13)	3m 47s
linux (opensuse/leap:latest, clang gcc11-c++, CC=clang CXX=clang++)	3m 25s
macos (macos-14)	1m 41s
linux (opensuse/tumbleweed, gcc gcc-c++)	2m 58s
macos (macos-15)	1m 43s
linux (opensuse/tumbleweed, clang, CC=clang CXX=clang++)	3m 3s
linux (archlinux:base, gcc)	2m 55s
linux (archlinux:base, clang, CC=clang CXX=clang++)	2m 57s
linux (ubuntu:24.04, gcc-10 g++-10, CC=gcc-10 CXX=g++-10)	2m 9s
linux (ubuntu:24.04, clang-15 libstdc++-10-dev, CC=clang-15 CXX=clang++-15)	2m 53s
linux (alpine, gcc, CC=gcc CXX=g++)	2m 47s
linux (fedora:latest, gcc gcc-g++)	2m 32s
linux (fedora:rawhide, gcc gcc-g++)	2m 29s
	36m 44s

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