DOC: (de)type the return value of concat (#17079)
Was being parsed by Pycharm as being type "type".

 - [ ] closes #17079
 - [ ] tests added / passed
 - [ ] passes ``git diff upstream/master -u -- "*.py" | flake8 --diff``
 - [ ] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=h1) Report
> Merging [#17119](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b03f7e52e859c5d20141a47aa4d6880a321af84d?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17119/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17119      +/-   ##
==========================================
- Coverage   91.02%   91.01%   -0.02%     
==========================================
  Files         161      161              
  Lines       49397    49397              
==========================================
- Hits        44966    44957       -9     
- Misses       4431     4440       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.78% <ø> (ø)` | :arrow_up: |
| #single | `40.28% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/reshape/concat.py](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9jb25jYXQucHk=) | `97.62% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.66% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17119?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/17119?src=pr&el=footer). Last update [b03f7e5...a2739b7](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=h1) Report
> Merging [#17119](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b03f7e52e859c5d20141a47aa4d6880a321af84d?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17119/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17119      +/-   ##
==========================================
- Coverage   91.02%   91.01%   -0.02%     
==========================================
  Files         161      161              
  Lines       49397    49397              
==========================================
- Hits        44966    44957       -9     
- Misses       4431     4440       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.78% <ø> (ø)` | :arrow_up: |
| #single | `40.28% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/reshape/concat.py](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9jb25jYXQucHk=) | `97.62% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.66% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17119?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/17119?src=pr&el=footer). Last update [b03f7e5...a2739b7](https://codecov.io/gh/pandas-dev/pandas/pull/17119?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!