Update definitions.py

I think commit 05cef2e changed the Handle class to HandleElem but not all references were updated. 

I noticed that even with this change, the CI still passed. Is there enough code coverage to ensure this would have been caught?

Author: patrickhuber

design/mvp/canonical-abi/definitions.py

@@ -279,7 +279,7 @@ def num_i32_flags(labels):
 class CallContext:
   opts: CanonicalOptions
   inst: ComponentInstance
-  lenders: [Handle]
+  lenders: [HandleElem]
   borrow_count: int
 
   def __init__(self, opts, inst):