Fix Series construction with dtype=str
TST: Added test for construction Series with dtype=str 
BUG: Handles case where data is scalar 
DOC: added changes to whatsnew/v0.23.0.txt

Checklist for other PRs (remove this part if you are doing a PR for the pandas documentation sprint):

- [x] closes #19853
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20401?src=pr&el=h1) Report
> Merging [#20401](https://codecov.io/gh/pandas-dev/pandas/pull/20401?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/bd8a3cffd70dabeb458099a9d5477d3d913439cc?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20401/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/20401?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20401      +/-   ##
==========================================
+ Coverage   91.77%   91.77%   +<.01%     
==========================================
  Files         152      152              
  Lines       49203    49214      +11     
==========================================
+ Hits        45155    45168      +13     
+ Misses       4048     4046       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.16% <100%> (ø)` | :arrow_up: |
| #single | `41.84% <100%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20401?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/20401/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `93.85% <100%> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/20401/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `84.11% <0%> (+0.37%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20401?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/20401?src=pr&el=footer). Last update [bd8a3cf...41d35ca](https://codecov.io/gh/pandas-dev/pandas/pull/20401?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jreback any more comments here? thanks @nikoskaragiannakis 