[CI][IOS] Rename the IOS_VERSION (#46645)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46645
### Summary
The IOS_VERSION should be renamed to XCODE_VERSION
### Test
- CircleCI
Test Plan: Imported from OSS
Reviewed By: seemethere, linbinyu
Differential Revision: D24459598
Pulled By: xta0
fbshipit-source-id: 9dcba973cc57aa44f8fd4151daf5d89c8da61c67
