[pre-commit.ci] auto fixes from pre-commit.com hooks

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Author: pre-commit-ci[bot]

xarray/conventions.py

@@ -10,7 +10,7 @@
 
 from xarray.coding import strings, times, variables
 from xarray.coding.variables import SerializationWarning, pop_to
-from xarray.core import duck_array_ops, indexing
+from xarray.core import indexing
 from xarray.core.common import (
     _contains_datetime_like_objects,
     contains_cftime_datetimes,