use new stages names to silence pre-commit warning

[JulienGrv]

This fixes following warning:

[INFO] Initializing environment for https://github.com/scop/pre-commit-shfmt.
[WARNING] repo `https://github.com/scop/pre-commit-shfmt` uses deprecated stage names (commit, merge-commit, push) which will be removed in a future version.  Hint: often `pre-commit autoupdate --repo https://github.com/scop/pre-commit-shfmt` will fix this.  if it does not -- consider reporting an issue to that repo.
[INFO] Installing environment for https://github.com/scop/pre-commit-shfmt.

[scop]

I believe (but have not verified) that doing this would mean that the hooks would no longer work with pre-commit < 4. If so, I'm inclined to not make this change yet.

[JulienGrv]

Hi @scop , AFAIK the warnings were introduced with version 4.0 but the new names are there since version 3.2. Anyway, I don't mind leaving this PR opened until you think the time is right

[scop]

Thanks for the info, looks like the "new" names are available since 3.2.0 indeed, which I think is old enough for this change.

[scop]

Thanks!

[lucasfijen]

Hey! Nice to see you already merged a fix for the deprecation warnings.
Is there any chance on a new release for this hook so we can get rid of these warnings?:)

[scop]

v3.10.0-2 tagged now.