BUG: groupby-rolling with a timedelta
closes #13966
xref to #15130, closed by #15175

@chrisaycock  # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16091?src=pr&el=h1) Report
> Merging [#16091](https://codecov.io/gh/pandas-dev/pandas/pull/16091?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f5623087f010c21d1ccd618881e308ccf3b6d1b0?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16091/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/16091?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16091      +/-   ##
==========================================
+ Coverage   90.84%   90.84%   +<.01%     
==========================================
  Files         159      159              
  Lines       50776    50776              
==========================================
+ Hits        46128    46129       +1     
+ Misses       4648     4647       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.62% <ø> (ø)` | :arrow_up: |
| #single | `40.35% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16091?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16091?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.03% <0%> (+0.34%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16091?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/16091?src=pr&el=footer). Last update [f562308...b30a50f](https://codecov.io/gh/pandas-dev/pandas/pull/16091?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/16091?src=pr&el=h1) Report
> Merging [#16091](https://codecov.io/gh/pandas-dev/pandas/pull/16091?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f5623087f010c21d1ccd618881e308ccf3b6d1b0?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16091/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/16091?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #16091   +/-   ##
=======================================
  Coverage   90.84%   90.84%           
=======================================
  Files         159      159           
  Lines       50776    50776           
=======================================
  Hits        46128    46128           
  Misses       4648     4648
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.62% <ø> (ø)` | :arrow_up: |
| #single | `40.35% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16091?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/16091?src=pr&el=footer). Last update [f562308...b30a50f](https://codecov.io/gh/pandas-dev/pandas/pull/16091?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
