Try to include macos13

.github/workflows/mcstas-basictest.yml

@@ -22,6 +22,7 @@ jobs:
           - { os: ubuntu-24.04,  CC: clang,    CXX: clang++,    python: '3.12'  }
           - { os: ubuntu-22.04,  CC: clang,    CXX: clang++,    python: '3.11'  }
           - { os: ubuntu-22.04,  CC: gcc-12,   CXX: g++-12,     python: '3.11'  }
+          - { os: macos-13,      CC: clang,    CXX: clang++,    python: "3.11"  }
           - { os: macos-14,      CC: clang,    CXX: clang++,    python: "3.12"  }
           - { os: macos-15,      CC: clang,    CXX: clang++,    python: "3.13"  }
           - { os: windows-latest,  CC: gcc,    CXX: g++,        python: "3.12"  }
@@ -91,7 +92,9 @@ jobs:
            mkdir build_mcstas
            cd build_mcstas
            export EXTRA_ARGS_FOR_CMAKE=""
-           if [ "$RUNNER_OS" == "macOS" ]; then export EXTRA_ARGS_FOR_CMAKE="-DBISON_EXECUTABLE=/opt/homebrew/opt/bison/bin/bison -DFLEX_EXECUTABLE=/opt/homebrew/opt/flex/bin/flex"; fi
+           if [ "$RUNNER_OS" == "macOS" ]; then; if [ -d "/opt/homebrew/opt" ]; then export HOMEBRW="/opt/homebrew/opt"; fi; fi;
+           if [ "$RUNNER_OS" == "macOS" ]; then; if [ -d "/usr/local/opt" ]; then export HOMEBRW="/usr/local/opt"; fi; fi;
+           if [ "$RUNNER_OS" == "macOS" ]; then export EXTRA_ARGS_FOR_CMAKE="-DBISON_EXECUTABLE=${HOMEBRW}/bison/bin/bison -DFLEX_EXECUTABLE=${HOMEBRW}/flex/bin/flex"; fi
            if [ "$RUNNER_OS" == "Linux" ]; then export EXTRA_ARGS_FOR_CMAKE="-DNEXUSLIB=/usr/lib -DNEXUSINCLUDE=/usr/include/nexus"; fi
            cmake \
                -DCMAKE_INSTALL_PREFIX=../install_mcstas \