Revert "Change push CI to run on workflow_run event"

[ydshieh]

Reverts #17692

Really sorry, but the notification_service.py has error

Traceback (most recent call last):
  File "utils/notification_service.py", line 766, in <module>
    ci_author = ci_details["author"]["login"]
KeyError: 'author'

as the GH event is no longer coupled with a commit, and we lose some information about commit/author.
I need to change more things.

(On my own repo for testing, there is no notification_service.py. And this change of workflow_run can only be verified when being merged to main)

[sgugger]

Hope to have it back soon 😢

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[ydshieh]

merged to avoid further test failures