[CI] Disable ios-12-5-1-x86-64 (#81612)
Currently broken, but for a while it was not testing trunk, but rather some old released build, see https://github.com/pytorch/pytorch/runs/7369514831?check_suite_focus=true#step:9:147
Pull Request resolved: https://github.com/pytorch/pytorch/pull/81612
Approved by: https://github.com/kit1980
