Backport PR #47581 on branch 1.4.x (BUG: DataFrame.loc not aligning rhs df for single block case)
Backport PR #47581

cc @simonjayhawkins 

WIll put up a pr for the whatsnew later
> we need to check whether #47361 was a regression first

sorry, meant #47216 OK if not a regression then not necessarily an issue as we can still do bug fixes in patch releases. don't merge yet, I'll look again tomorrow. If we go with the original commit in this PR we should probably do it as 2 separate backports.  Yep, if we do both then separate.

I would just do the regression here. It's close to 1.5 anyway. The change compared to main is not that big