BUG: fix tzaware dataframe transpose bug
State: closed

This allows us to get rid of a bunch of xfails and FIXMEs in arithmetic tests.  Changes in groupby are the most likely to need attention; this is not an area of the code I know well.

Not sure if TestTranspose belongs somewhere else.  Suggestions welcome.

Split a couple of too-widely-scoped groupby tests.

Will follow-up with issues this closes, whatsnew entry, and GH references added to tests.

xref #23988

- [x] closes #13287
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry


Labels:
name: Bug
name: Datetime
description: Datetime data dtype
name: DataFrame
description: DataFrame data structure

Comments:
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26825?src=pr&el=h1) Report
> Merging [#26825](https://codecov.io/gh/pandas-dev/pandas/pull/26825?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a7f1d69b135bbbf649cf1af9a62d79acb963e47c?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26825/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26825?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26825      +/-   ##
==========================================
- Coverage   92.01%      92%   -0.01%     
==========================================
  Files         180      180              
  Lines       50754    50766      +12     
==========================================
+ Hits        46699    46708       +9     
- Misses       4055     4058       +3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.64% <100%> (ø)` | :arrow_up: |
| #single | `41.84% <35%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26825?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/groupby/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/26825/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9nZW5lcmljLnB5) | `89.37% <100%> (+0.04%)` | :arrow_up: |
| [pandas/core/internals/construction.py](https://codecov.io/gh/pandas-dev/pandas/pull/26825/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2NvbnN0cnVjdGlvbi5weQ==) | `96.04% <100%> (+0.08%)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26825/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `88.88% <0%> (-11.12%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26825/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.89% <0%> (-0.12%)` | :arrow_down: |
| [pandas/core/sorting.py](https://codecov.io/gh/pandas-dev/pandas/pull/26825/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc29ydGluZy5weQ==) | `98.35% <0%> (ø)` | :arrow_up: |
| [pandas/compat/\_optional.py](https://codecov.io/gh/pandas-dev/pandas/pull/26825/diff?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9fb3B0aW9uYWwucHk=) | `100% <0%> (ø)` | :arrow_up: |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/26825/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `90.89% <0%> (+0.16%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26825?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26825?src=pr&el=footer). Last update [a7f1d69...8b2372e](https://codecov.io/gh/pandas-dev/pandas/pull/26825?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

Updated with requested edit, GH references in tests, and whatsnew.
@jreback anything else here actionable?
haven’t had a chance to relook
I think comments have been addressed.