Switch nightly jobs to trigger on 'nightly' branch rather than cron. (#26830)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26830
Fixes #26817
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Differential Revision: D17608535
Pulled By: ezyang
fbshipit-source-id: 18b47af508bd606391b1e6436cefe586b9926ace
