Fix DatetimeAccessor strftime errors due to upstream changes (#10550)

Author: spencerkclark

xarray/core/accessor_dt.py

@@ -206,7 +206,7 @@ def _strftime_through_cftimeindex(values, date_format: str):
     values_as_cftimeindex = CFTimeIndex(duck_array_ops.ravel(values))
 
     field_values = values_as_cftimeindex.strftime(date_format)
-    return field_values.values.reshape(values.shape)
+    return field_values.to_numpy().reshape(values.shape)
 
 
 def _strftime_through_series(values, date_format: str):
@@ -215,7 +215,7 @@ def _strftime_through_series(values, date_format: str):
     """
     values_as_series = pd.Series(duck_array_ops.ravel(values), copy=False)
     strs = values_as_series.dt.strftime(date_format)
-    return strs.values.reshape(values.shape)
+    return strs.to_numpy().reshape(values.shape)
 
 
 def _strftime(values, date_format):