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])