fix pandas-dev tests (#3491)

* Don't initialize DataArrays with Pandas attrs.

* re-enable pandas-dev CI.

Author: dcherian

ci/azure/install.yml

@@ -16,7 +16,7 @@ steps:
         --pre \
         --upgrade \
         matplotlib \
-        pandas=0.26.0.dev0+628.g03c1a3db2 \  # FIXME https://github.com/pydata/xarray/issues/3440
+        pandas \
         scipy
         # numpy \  # FIXME https://github.com/pydata/xarray/issues/3409
     pip install \

xarray/core/dataarray.py

@@ -51,6 +51,7 @@
 from .dataset import Dataset, merge_indexes, split_indexes
 from .formatting import format_item
 from .indexes import Indexes, default_indexes
+from .merge import PANDAS_TYPES
 from .options import OPTIONS
 from .utils import Default, ReprObject, _check_inplace, _default, either_dict_or_kwargs
 from .variable import (
@@ -357,7 +358,7 @@ def __init__(
                 dims = getattr(data, "dims", getattr(coords, "dims", None))
             if name is None:
                 name = getattr(data, "name", None)
-            if attrs is None:
+            if attrs is None and not isinstance(data, PANDAS_TYPES):
                 attrs = getattr(data, "attrs", None)
             if encoding is None:
                 encoding = getattr(data, "encoding", None)