Avoid extra read from disk when creating Pandas Index. (#8893)

* Avoid extra read from disk when creating Pandas Index.

* Update xarray/core/indexes.py

Co-authored-by: Maximilian Roos <5635139+max-sixty@users.noreply.github.com>

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Co-authored-by: Maximilian Roos <5635139+max-sixty@users.noreply.github.com>

xarray/core/indexes.py

@@ -632,7 +632,8 @@ def from_variables(
         # the checks below.
 
         # preserve wrapped pd.Index (if any)
-        data = getattr(var._data, "array", var.data)
+        # accessing `.data` can load data from disk, so we only access if needed
+        data = getattr(var._data, "array") if hasattr(var._data, "array") else var.data
         # multi-index level variable: get level index
         if isinstance(var._data, PandasMultiIndexingAdapter):
             level = var._data.level