### What changes were proposed in this pull request?
This PR proposes to use Python 3.9 in documentation and linter at GitHub Actions. This PR also contains the fixes for mypy check (introduced by Python 3.9 upgrade)
```
python/pyspark/sql/pandas/_typing/protocols/frame.pyi:64: error: Name "np.ndarray" is not defined
python/pyspark/sql/pandas/_typing/protocols/frame.pyi:91: error: Name "np.recarray" is not defined
python/pyspark/sql/pandas/_typing/protocols/frame.pyi:165: error: Name "np.ndarray" is not defined
python/pyspark/pandas/categorical.py:82: error: Item "dtype[Any]" of "Union[dtype[Any], Any]" has no attribute "categories"
python/pyspark/pandas/categorical.py:109: error: Item "dtype[Any]" of "Union[dtype[Any], Any]" has no attribute "ordered"
python/pyspark/ml/linalg/__init__.pyi:184: error: Return type "ndarray[Any, Any]" of "toArray" incompatible with return type "NoReturn" in supertype "Matrix"
python/pyspark/ml/linalg/__init__.pyi:217: error: Return type "ndarray[Any, Any]" of "toArray" incompatible with return type "NoReturn" in supertype "Matrix"
python/pyspark/pandas/typedef/typehints.py:163: error: Module has no attribute "bool"; maybe "bool_" or "bool8"?
python/pyspark/pandas/typedef/typehints.py:174: error: Module has no attribute "float"; maybe "float_", "cfloat", or "float96"?
python/pyspark/pandas/typedef/typehints.py:180: error: Module has no attribute "int"; maybe "uint", "rint", or "intp"?
python/pyspark/pandas/ml.py:81: error: Value of type variable "_DTypeScalar_co" of "dtype" cannot be "object"
python/pyspark/pandas/indexing.py:1649: error: Module has no attribute "int"; maybe "uint", "rint", or "intp"?
python/pyspark/pandas/indexing.py:1656: error: Module has no attribute "int"; maybe "uint", "rint", or "intp"?
python/pyspark/pandas/frame.py:4969: error: Function "numpy.array" is not valid as a type
python/pyspark/pandas/frame.py:4969: note: Perhaps you need "Callable[...]" or a callback protocol?
python/pyspark/pandas/frame.py:4970: error: Function "numpy.array" is not valid as a type
python/pyspark/pandas/frame.py:4970: note: Perhaps you need "Callable[...]" or a callback protocol?
python/pyspark/pandas/frame.py:7402: error: "List[Any]" has no attribute "tolist"
python/pyspark/pandas/series.py:1030: error: Module has no attribute "_NoValue"
python/pyspark/pandas/series.py:1031: error: Module has no attribute "_NoValue"
python/pyspark/pandas/indexes/category.py:159: error: Item "dtype[Any]" of "Union[dtype[Any], Any]" has no attribute "categories"
python/pyspark/pandas/indexes/category.py:180: error: Item "dtype[Any]" of "Union[dtype[Any], Any]" has no attribute "ordered"
python/pyspark/pandas/namespace.py:2036: error: Argument 1 to "column_name" has incompatible type "float"; expected "str"
python/pyspark/pandas/mlflow.py:59: error: Incompatible types in assignment (expression has type "Type[floating[Any]]", variable has type "str")
python/pyspark/pandas/data_type_ops/categorical_ops.py:43: error: Item "dtype[Any]" of "Union[dtype[Any], Any]" has no attribute "categories"
python/pyspark/pandas/data_type_ops/categorical_ops.py:43: error: Item "dtype[Any]" of "Union[dtype[Any], Any]" has no attribute "ordered"
python/pyspark/pandas/data_type_ops/categorical_ops.py:56: error: Item "dtype[Any]" of "Union[dtype[Any], Any]" has no attribute "categories"
python/pyspark/pandas/tests/test_typedef.py:70: error: Name "np.float" is not defined
python/pyspark/pandas/tests/test_typedef.py:77: error: Name "np.float" is not defined
python/pyspark/pandas/tests/test_typedef.py:85: error: Name "np.float" is not defined
python/pyspark/pandas/tests/test_typedef.py💯 error: Name "np.float" is not defined
python/pyspark/pandas/tests/test_typedef.py:108: error: Name "np.float" is not defined
python/pyspark/mllib/clustering.pyi:152: error: Incompatible types in assignment (expression has type "ndarray[Any, Any]", base class "KMeansModel" defined the type as "List[ndarray[Any, Any]]")
python/pyspark/mllib/classification.pyi:93: error: Signature of "predict" incompatible with supertype "LinearClassificationModel"
Found 32 errors in 15 files (checked 315 source files)
1
```
### Why are the changes needed?
Python 3.6 is deprecated at SPARK-35938
### Does this PR introduce _any_ user-facing change?
No. Maybe static analysis, etc. by some type hints but they are really non-breaking..
### How was this patch tested?
I manually checked by GitHub Actions build in forked repository.
Closes#33356 from HyukjinKwon/SPARK-36146.
Authored-by: Hyukjin Kwon <gurwls223@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
a71dd6af2f