Adding back type ignores

This is cargo-cult.  I wonder if there's a different CI test that wanted these
and since this is now excluded at the top level.  I'm putting them back until
migration into main codebase.

xarray/datatree_/datatree/io.py

@@ -1,16 +1,16 @@
-from .datatree import DataTree
+from xarray.datatree_.datatree import DataTree
 
 
 def _get_nc_dataset_class(engine):
     if engine == "netcdf4":
-        from netCDF4 import Dataset
+        from netCDF4 import Dataset  # type: ignore
     elif engine == "h5netcdf":
-        from h5netcdf.legacyapi import Dataset
+        from h5netcdf.legacyapi import Dataset  # type: ignore
     elif engine is None:
         try:
             from netCDF4 import Dataset
         except ImportError:
-            from h5netcdf.legacyapi import Dataset
+            from h5netcdf.legacyapi import Dataset  # type: ignore
     else:
         raise ValueError(f"unsupported engine: {engine}")
     return Dataset