BUG: Fix Series constructor when copy=True
Updates Series constructor to include copy argument when dtype argument
is also provided. Adds tests for copy parameter.

xref #15125

 - [x] closes #15125
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master | flake8 --diff``
 - [x] whatsnew entry

minor comments. ping when updated / green. ## [Current coverage](https://codecov.io/gh/pandas-dev/pandas/pull/15128?src=pr) is 85.53% (diff: 100%)
> Merging [#15128](https://codecov.io/gh/pandas-dev/pandas/pull/15128?src=pr) into [master](https://codecov.io/gh/pandas-dev/pandas/branch/master?src=pr) will decrease coverage by **<.01%**

```diff
@@             master     #15128   diff @@
==========================================
  Files           145        145          
  Lines         51288      51288          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
- Hits          43872      43871     -1   
- Misses         7416       7417     +1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [1f82f18...7b0c959](https://codecov.io/gh/pandas-dev/pandas/compare/1f82f18933e42f0c9695b551cfce98cd1632f841...7b0c959930ae0e10d62a40520a7fed7b3ad9eff6?src=pr) Thanks for pointing out the anti-pattern, @jreback. All green now. Let me know if you see any other changes. thanks!