Refresh GitHub workflow matrix.

[ueshin]

Now that Spark 3.1 has been released, we should refresh GitHub Action's workflow matrix to focus more on the newer versions.

The new matrix:

Python	PySpark	pandas	PyArrow
3.5	2.3.4	0.23.4	0.16.0
3.6	2.3.4	0.24.2	0.10.0
3.6	2.4.7	0.24.2	0.14.1
3.7	2.4.7	0.25.3	0.15.1
3.7	3.0.2	1.0.5	1.0.1
3.7	3.1.1	1.1.5	2.0.0
3.8	3.0.2	1.1.5	2.0.0
3.8	3.1.1	1.2.3	3.0.0

[HyukjinKwon]

Yeah, sounds good if tests pass.

[codecov-io]

Codecov Report

Merging #2083 (57add74) into master (9150ca4) will decrease coverage by 0.96%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2083      +/-   ##
==========================================
- Coverage   95.27%   94.31%   -0.97%     
==========================================
  Files          57       57              
  Lines       13196    13219      +23     
==========================================
- Hits        12573    12467     -106     
- Misses        623      752     +129     

Impacted Files	Coverage Δ
databricks/koalas/internal.py	95.31% <ø> (-1.31%)	⬇️
databricks/koalas/indexes/multi.py	93.40% <100.00%> (-0.44%)	⬇️
databricks/koalas/usage_logging/__init__.py	26.66% <0.00%> (-65.84%)	⬇️
databricks/koalas/usage_logging/usage_logger.py	47.82% <0.00%> (-52.18%)	⬇️
databricks/conftest.py	92.18% <0.00%> (-7.82%)	⬇️
databricks/koalas/typedef/typehints.py	87.70% <0.00%> (-6.71%)	⬇️
databricks/koalas/__init__.py	88.00% <0.00%> (-4.00%)	⬇️
databricks/koalas/tests/indexes/test_datetime.py	96.92% <0.00%> (-3.08%)	⬇️
databricks/koalas/indexes/datetimes.py	96.58% <0.00%> (-1.52%)	⬇️
... and 2 more

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[ueshin]

Let me merge this now. Please feel free to leave comments if any. Thanks.