CI: bump to GCC 14 for building macOS binaries

scripts/homebrew-native-arm64.ini

 # Meson native file for compiling under Homebrew / arm64
 
 [binaries]
-cpp = '/opt/homebrew/bin/g++-13'
+cpp = '/opt/homebrew/bin/g++-14'
 flex = '/opt/homebrew/opt/flex/bin/flex'
 bison = '/opt/homebrew/opt/bison/bin/bison'
 

scripts/homebrew-native-x86_64.ini

 # Meson native file for compiling under Homebrew / x86-64
 
 [binaries]
-cpp = '/usr/local/bin/g++-13'
+cpp = '/usr/local/bin/g++-14'
 flex = '/usr/local/opt/flex/bin/flex'
 bison = '/usr/local/opt/bison/bin/bison'