BUG: first("2M") returning incorrect results
- [x] closes #29623
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
 
This would fix #29623 for offsets with n > 1
cc @simonjayhawkins 
Thanks @phofl for the quick response.

I'm not sure where this leaves us w.r.t. backports. whether we should backport #38331 (i.e. reopen #38436) and then backport this as well.

or let these changes sit in master for a while (and move release note added in #38331 to 1.3 whatsnew) If we decide to backport, we could cherry pick this one on top of the other Commit. But I am not quite sure either if we should backport. we can just revert the original and then merge to master  Oh right, that would work. Should I open a Revert PR? #38448 Ok, thx. Will adjust this one after the other is merged after the revert is merged, will reopen issue and change milestone. so can update the OP here to close issue again. Done. This fixes both cases now. thanks @phofl 