[CIFlow] Modify workflow trigger logic (#65733)
Summary:
CIFLow workflows should always run on push event
On pull-request workflow should run if label conditions are met or if
no `ciflow/` labels are associated with it, workflow is enabled by
default
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65733
Reviewed By: zhouzhuojie
Differential Revision: D31251278
Pulled By: malfet
fbshipit-source-id: 31ce745cb224df7c6fec1682ec4180513e3dadf3
