SilhouetteScore C++ tests seed

[divyegala]

As @hcho3 noted, a BatchedSilhouetteScore C++ test failed in CI with flakiness. Setting the seed ensures this won't happen

[dantegd]

@divyegala since this is not for merging, can you change this to a draft PR?

[codecov-io]

Codecov Report

Merging #3640 (10cb321) into branch-0.19 (fd9ec89) will increase coverage by 0.49%.
The diff coverage is 92.59%.

❗ Current head 10cb321 differs from pull request most recent head f552b0b. Consider uploading reports for the commit f552b0b to get more accurate results

@@               Coverage Diff               @@
##           branch-0.19    #3640      +/-   ##
===============================================
+ Coverage        80.70%   81.20%   +0.49%     
===============================================
  Files              227      228       +1     
  Lines            17615    17869     +254     
===============================================
+ Hits             14217    14511     +294     
+ Misses            3398     3358      -40     

Flag	Coverage Δ
dask	45.31% <34.81%> (+0.32%)	⬆️
non-dask	73.28% <92.59%> (+0.36%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
python/cuml/cluster/kmeans.pyx	91.95% <ø> (ø)
...ython/cuml/dask/ensemble/randomforestclassifier.py	62.76% <ø> (+6.35%)	⬆️
python/cuml/fil/fil.pyx	92.85% <ø> (+1.02%)	⬆️
python/cuml/neighbors/__init__.py	100.00% <ø> (ø)
python/cuml/preprocessing/encoders.py	95.10% <ø> (+0.02%)	⬆️
python/cuml/common/memory_utils.py	79.26% <50.00%> (+0.15%)	⬆️
python/cuml/neighbors/ann.pyx	90.80% <80.00%> (+29.17%)	⬆️
python/cuml/solvers/qn.pyx	97.20% <85.71%> (-0.43%)	⬇️
python/cuml/linear_model/logistic_regression.pyx	89.16% <88.88%> (+0.20%)	⬆️
python/cuml/ensemble/randomforestclassifier.pyx	73.40% <100.00%> (-0.09%)	⬇️
... and 57 more

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[divyegala]

@dantegd can you review?

[dantegd]

@gpucibot merge