Fix formatting bug in AbstractAlembicTest class

Replace `formatstring, value` with the correct `formatstring % value`.

No functional changes to any actual tests.

tests/python/alembic_tests.py

@@ -105,7 +105,7 @@ class AbstractAlembicTest(AbstractBlenderRunnerTest):
                 # To read those, call self.abcprop() on it.
                 continue
             if len(parts) < 2:
-                raise ValueError('Error parsing result from abcprop: %s', info.strip())
+                raise ValueError('Error parsing result from abcprop: %s' % info.strip())
             valtype_and_arrsize, name_and_extent = parts[1:]
 
             # Parse name and extent