add attempt to import ValidationError

first try to import ValidationError from
asdf.exceptions then fallback to importing
from the top level asdf if this fails.

dkist/dataset/loader.py

@@ -5,7 +5,10 @@
 from parfive import Results
 
 import asdf
-from asdf.exceptions import ValidationError
+try:
+    from asdf.exceptions import ValidationError
+except ImportError:
+    from asdf import ValidationError
 
 
 @singledispatch

setup.cfg

@@ -22,9 +22,9 @@ packages = find:
 include_package_data = True
 install_requires =
   appdirs>=1.4
-  asdf>=2.15.1
+  asdf>=2.9.2
   asdf-astropy>=0.1.1
-  asdf-transform-schemas>=0.3
+  asdf-transform-schemas
   astropy>=5
   dask[array]>=2021.8.0
   globus-sdk>=3.0