Zonal_crosstab 3D: Ensure content of input param `values` is preserved

[thuydotm]

Fixes #751

[codecov-commenter]

Codecov Report

Base: 79.87% // Head: 79.88% // Increases project coverage by +0.00% :tada:

Coverage data is based on head (363457d) compared to base (f6c5164). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #754 +/- ## ======================================= Coverage 79.87% 79.88% ======================================= Files 19 19 Lines 4169 4170 +1 ======================================= + Hits 3330 3331 +1 Misses 839 839 ``` | [Impacted Files](https://codecov.io/gh/makepath/xarray-spatial/pull/754?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=makepath) | Coverage Δ | | |---|---|---| | [xrspatial/zonal.py](https://codecov.io/gh/makepath/xarray-spatial/pull/754?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=makepath#diff-eHJzcGF0aWFsL3pvbmFsLnB5) | `85.47% <100.00%> (+0.02%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=makepath). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=makepath)

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[brendancol]

@thuydotm

• [x] Add test case to test_zonal to make sure input values remain unmodified