DOC: Fix SA01 errors for pandas.Index.astype (#58352)

* pandas.Index.astype * check fixes * series to index

Author: Nrezhang

ci/code_checks.sh

@@ -129,7 +129,6 @@ if [[ -z "$CHECK" || "$CHECK" == "docstrings" ]]; then
  -i "pandas.Index PR07" \
  -i "pandas.Index.T SA01" \
  -i "pandas.Index.append PR07,RT03,SA01" \
- -i "pandas.Index.astype SA01" \
  -i "pandas.Index.copy PR07,SA01" \
  -i "pandas.Index.difference PR07,RT03,SA01" \
  -i "pandas.Index.drop PR07,SA01" \

pandas/core/indexes/base.py

@@ -1060,6 +1060,12 @@ def astype(self, dtype, copy: bool = True):
  Index
  Index with values cast to specified dtype.
 
+ See Also
+ --------
+ Index.dtype: Return the dtype object of the underlying data.
+ Index.dtypes: Return the dtype object of the underlying data.
+ Index.convert_dtypes: Convert columns to the best possible dtypes.
+
  Examples
  --------
  >>> idx = pd.Index([1, 2, 3])