Adds time index type check compatible with py3.6

Pandas dropped support for python 3.6 in something like 1.2.
So pandas 1.1.5 is what we're using in our CI system, and that
does not have the `NDArrayBackedExtensionIndex` type.

So I'm guessing here, but looking at the 1.1.5 source, we instead
want `ExtensionIndex`.

hamilton/base.py

@@ -64,7 +64,11 @@ def pandas_index_types(
         for output_name, output_value in outputs.items():
             if isinstance(output_value, (pd.DataFrame, pd.Series)):
                 dict_key = f"{output_value.index.__class__.__name__}:::{output_value.index.dtype}"
-                if isinstance(output_value.index, pd_extension.NDArrayBackedExtensionIndex):
+                try:
+                    index_type = getattr(pd_extension, "NDArrayBackedExtensionIndex")
+                except AttributeError:  # for python 3.6 & pandas 1.1.5
+                    index_type = getattr(pd_extension, "ExtensionIndex")
+                if isinstance(output_value.index, index_type):
                     # it's a time index -- these will produce garbage if not aligned properly.
                     time_indexes[dict_key].append(output_name)
             else: