BUG: Keep original name in str.cat
Closes https://github.com/pandas-dev/pandas/issues/21053

cc @jreback @jorisvandenbossche @h-vetinari for a quick check if you have a chance.
lgtm The circle failure appears to be unrelated. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21054?src=pr&el=h1) Report
> Merging [#21054](https://codecov.io/gh/pandas-dev/pandas/pull/21054?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8aff1243a54fecf6002268d5bafe1c893067bf37?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21054/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/21054?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #21054   +/-   ##
=======================================
  Coverage   91.82%   91.82%           
=======================================
  Files         153      153           
  Lines       49503    49503           
=======================================
  Hits        45458    45458           
  Misses       4045     4045
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.22% <100%> (ø)` | :arrow_up: |
| #single | `41.88% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21054?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/21054/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.62% <100%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21054?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/21054?src=pr&el=footer). Last update [8aff124...6d19bca](https://codecov.io/gh/pandas-dev/pandas/pull/21054?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
