Fix list of testing requirements in setup.py.

[bdice]

The list of testing requirements was missing a comma in setup.py. This fixes it.

[codecov]

Codecov Report

Merging #10678 (bd39d73) into branch-22.06 (94a5d41) will increase coverage by 0.02%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           branch-22.06   #10678      +/-   ##
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+ Coverage         86.38%   86.41%   +0.02%     
================================================
  Files               142      142              
  Lines             22334    22334              
================================================
+ Hits              19294    19300       +6     
+ Misses             3040     3034       -6     

Impacted Files	Coverage Δ
python/cudf/cudf/core/column/string.py	89.22% <0.00%> (+0.12%)	⬆️
python/cudf/cudf/core/groupby/groupby.py	91.72% <0.00%> (+0.22%)	⬆️
python/cudf/cudf/core/tools/datetimes.py	84.49% <0.00%> (+0.30%)	⬆️
python/cudf/cudf/core/column/lists.py	92.79% <0.00%> (+1.27%)	⬆️

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[galipremsagar]

@gpucibot merge