libxml2: fix installation of Python bindings (#106575)
libxml2: fix installation of Python bindings (#106575)

We now pass `--install-lib` by default in `#setup_install_args`, but now
we need to be more specific about which Python to use when building.

See Homebrew/brew#13533 and #98809.
stgraber/homebrew-core,adam-moss/homebrew-core,stgraber/homebrew-core,lemzwerg/homebrew-core,Homebrew/homebrew-core,sjackman/homebrew-core,filcab/homebrew-core,Homebrew/homebrew-core,nandub/homebrew-core,zyedidia/homebrew-core,chrisfinazzo/homebrew-core,makigumo/homebrew-core,nbari/homebrew-core,nandub/homebrew-core,zyedidia/homebrew-core,adam-moss/homebrew-core,lemzwerg/homebrew-core,filcab/homebrew-core,sjackman/homebrew-core,chrisfinazzo/homebrew-core,nbari/homebrew-core,makigumo/homebrew-core