Update PEP 11 to promote aarch64-unknown-linux-gnu (gcc, glibc) to tier-1

[diegorusso]

Raising the issue here related to this PR: python/peps#4215

As reference I leave the full Discourse thread where this has been discussed: https://discuss.python.org/t/pep-11-proposal-to-promote-aarch64-plaftorms-to-tier-1/44774/30

[gpshead]

approved and PR merged.