[FIX] Add "double" type to allowed DisplacementFieldTransform (#3287)

The ANTs utility `CompositeTransformUtil --assemble` outputs its
displacement field as 'DisplacementFieldTransform_double_3_3', but
utils/transform/load_ants_h5 throws an error unless it is
'DisplacementFieldTransform_float_3_3'. Presumably this is just a check
to make sure it is a displacement field. The code after this check works
fine for "double".

fmriprep/utils/transforms.py

@@ -71,7 +71,10 @@ def load_ants_h5(filename: Path) -> nt.base.TransformBase:
     transform2 = h['TransformGroup']['2']
 
     # Confirm these transformations are applicable
-    if transform2['TransformType'][:][0] != b'DisplacementFieldTransform_float_3_3':
+    if transform2['TransformType'][:][0] not in (
+        b'DisplacementFieldTransform_float_3_3',
+        b'DisplacementFieldTransform_double_3_3',
+    ):
         msg = 'Unknown transform type [2]\n'
         for i in h['TransformGroup'].keys():
             msg += f'[{i}]: {h["TransformGroup"][i]["TransformType"][:][0]}\n'