CI: update pyupgrade to 2.7.4 in pre-commit
Updating pyupgrade to 2.7.4 in pre-commit yaml. `pre-commit run pyupgrade --all-files` runs good :+1: 

- [x] closes #37891
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
- [x] passes `pre-commit run pyupgrade --all-files`

Thanks @BAlmeidaS !

@jreback the automated weekly update job from #37362 didn't work: https://github.com/pandas-dev/pandas/actions/runs/365510411 
 
If you added the `ACTION_TRIGGER_TOKEN` secret token then I don't know why it failed, the logs don't give much away - in which case, I could remove the job and do it manually (as here) when there's an update (which isn't too bad anyway)