Error with .drop([]) on non-unique index
Wraps the labels array in `_ensure_object`. The labels array is being cast to a float by default, causing the error raised in #16398.

 - [X] closes #16398 
 - [X] tests added / passed
 - [X] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
 - [x] whatsnew entry

Where does the `whatsnew` entry go for this PR? This can be 0.20.2 since it's a bugfix Done, plz let me know if you need anything else on my end @lloydkirk can you update with a test and fix the note in the whatsnew? The test can go in `pandas/tests/frame/test_axis_select_reindex.py` # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=h1) Report
> Merging [#16428](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/49ec31bbaeca81a6f58fc1be26fe80f3ac188cdd?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16428/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16428      +/-   ##
==========================================
- Coverage   90.42%   90.42%   -0.01%     
==========================================
  Files         161      161              
  Lines       51023    51023              
==========================================
- Hits        46138    46137       -1     
- Misses       4885     4886       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.26% <100%> (-0.01%)` | :arrow_down: |
| #single | `40.17% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `92.13% <100%> (ø)` | :arrow_up: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.05% <0%> (-0.34%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16428?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/16428?src=pr&el=footer). Last update [49ec31b...1973925](https://codecov.io/gh/pandas-dev/pandas/pull/16428?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/16428?src=pr&el=h1) Report
> Merging [#16428](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/49ec31bbaeca81a6f58fc1be26fe80f3ac188cdd?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16428/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16428      +/-   ##
==========================================
- Coverage   90.42%   90.42%   -0.01%     
==========================================
  Files         161      161              
  Lines       51023    51023              
==========================================
- Hits        46138    46137       -1     
- Misses       4885     4886       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.26% <100%> (-0.01%)` | :arrow_down: |
| #single | `40.17% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `92.13% <100%> (ø)` | :arrow_up: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.05% <0%> (-0.34%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16428?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/16428?src=pr&el=footer). Last update [49ec31b...1973925](https://codecov.io/gh/pandas-dev/pandas/pull/16428?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Done, added a test to ``test_drop``, and to ``test_drop_names``, and fixed the whatsnew language thanks!