[ghactions] bump gcc version on mac os to 16, new default version from brew

Author: the-hampel

.github/workflows/build.yml

@@ -29,7 +29,7 @@ jobs:
           - { os: ubuntu-24.04, cc: clang-20, cxx: clang++-20, clang_cc: clang-20, clang_cxx: clang++-20 }
           - { os: ubuntu-24.04, cc: gcc-14, cxx: g++-14, clang_cc: clang-20, clang_cxx: clang++-20 }
           - { os: macos-15, cc: clang, cxx: clang++, clang_cc: clang, clang_cxx: clang++ }
-          - { os: macos-15, cc: gcc-15, cxx: g++-15, clang_cc: clang, clang_cxx: clang++ }
+          - { os: macos-15, cc: gcc-16, cxx: g++-16, clang_cc: clang, clang_cxx: clang++ }
 
     runs-on: ${{ matrix.os }}