fix typing (#10006)

Author: kmuehlbauer

xarray/core/dataset.py

@@ -9141,7 +9141,7 @@ def polyfit(
         lhs = np.vander(x, order)
 
         if rcond is None:
-            rcond = x.shape[0] * np.finfo(x.dtype).eps  # type: ignore[assignment]
+            rcond = x.shape[0] * np.finfo(x.dtype).eps
 
         # Weights:
         if w is not None:

xarray/core/dtypes.py

@@ -62,7 +62,7 @@ def maybe_promote(dtype: np.dtype) -> tuple[np.dtype, Any]:
     # N.B. these casting rules should match pandas
     dtype_: np.typing.DTypeLike
     fill_value: Any
-    if HAS_STRING_DTYPE and np.issubdtype(dtype, np.dtypes.StringDType()):  # type: ignore[attr-defined]
+    if HAS_STRING_DTYPE and np.issubdtype(dtype, np.dtypes.StringDType()):
         # for now, we always promote string dtypes to object for consistency with existing behavior
         # TODO: refactor this once we have a better way to handle numpy vlen-string dtypes
         dtype_ = object