add conda environment for CUDA 11.4

[seunghwak]

Add conda .yml file for CUDA 11.4 (mimicking cuML's rapidsai/cuml#4160).

[BradReesWork]

rerun tests

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (branch-21.10@4d4e571). Click here to learn what that means.
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❗ Current head 21bbc91 differs from pull request most recent head 93a00dc. Consider uploading reports for the commit 93a00dc to get more accurate results

@@               Coverage Diff               @@
##             branch-21.10    #1784   +/-   ##
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  Coverage                ?   59.70%           
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  Files                   ?       77           
  Lines                   ?     3541           
  Branches                ?        0           
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  Hits                    ?     2114           
  Misses                  ?     1427           
  Partials                ?        0           

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[BradReesWork]

@gpucibot merge