auto make pr for xla pinned hash (#77824)
see https://docs.google.com/document/d/1jRT-on-v8bcTCHD8aGFH7IuCDR7JL37GlP6Z2EYgmyk/edit#
add file with hash, add nightly job that makes a pr to update the hash, pr needs to be manually accepted (for now? maybe can get bot to approve it automatically later)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/77824
Approved by: https://github.com/janeyx99
