BUG: Concat with tz-aware and timedelta raises AttributeError
- [x] closes #12620
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

@jreback 's comment on #12620:

> should be handled at a slightly higher level.

I added number of `dtype` check logic in `tseries/common/_concat_compat`. But it should work on `base/common/_concat_compat`. Lmk which is preferable.
