Update Programming Language :: Python Versions to 3.8 & 3.9

[madsbk]

Just noticed that the classifiers of the python packages doesn't include Python v3.9 but includes Python v3.7. Fixed.

[codecov]

Codecov Report

Merging #10579 (0405d4c) into branch-22.06 (291fbcf) will increase coverage by 0.01%.
The diff coverage is n/a.

❗ Current head 0405d4c differs from pull request most recent head 3b937a6. Consider uploading reports for the commit 3b937a6 to get more accurate results

@@               Coverage Diff                @@
##           branch-22.06   #10579      +/-   ##
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+ Coverage         86.31%   86.33%   +0.01%     
================================================
  Files               140      140              
  Lines             22300    22300              
================================================
+ Hits              19249    19253       +4     
+ Misses             3051     3047       -4     

Impacted Files	Coverage Δ
python/cudf/cudf/core/column/string.py	89.10% <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	90.49% <0.00%> (+0.45%)	⬆️

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[galipremsagar]

@gpucibot merge