DOC: add disallowing of Series construction of len-1 list with index to whatsnew
Closes https://github.com/pandas-dev/pandas/issues/20391
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20392?src=pr&el=h1) Report
> Merging [#20392](https://codecov.io/gh/pandas-dev/pandas/pull/20392?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/699a48bcd71da54da05caee85e5d006afabc3df6?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20392/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/20392?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20392      +/-   ##
==========================================
- Coverage   91.79%   91.77%   -0.03%     
==========================================
  Files         152      152              
  Lines       49205    49205              
==========================================
- Hits        45169    45157      -12     
- Misses       4036     4048      +12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.15% <ø> (-0.03%)` | :arrow_down: |
| #single | `41.85% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20392?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/20392/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.07% <0%> (-1.74%)` | :arrow_down: |
| [pandas/core/resample.py](https://codecov.io/gh/pandas-dev/pandas/pull/20392/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzYW1wbGUucHk=) | `96.43% <0%> (ø)` | :arrow_up: |
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/20392/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.32% <0%> (ø)` | :arrow_up: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20392?src=pr&el=footer). Last update [699a48b...a870f86](https://codecov.io/gh/pandas-dev/pandas/pull/20392?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
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