Fix OrderField's copy constructor

OrderField's copy constructor has a typo in the constructor to call.
This commit fixes it to refer to OrderField's constructor.

Reviewed By: tnfchris

Differential Revision: https://reviews.llvm.org/D94839

Author: Thomas Preud'homme

lnt/server/db/testsuite.py

@@ -292,7 +292,7 @@ def __repr__(self):
         return '%s%r' % (self.__class__.__name__, (self.name, self.ordinal))
 
     def __copy__(self):
-        return Ordinal(self.name, self.ordinal)
+        return OrderField(self.name, self.ordinal)
 
 
 class RunField(FieldMixin, Base):