Update tuf/ngclient/_internal/trusted_metadata_set.py

Co-authored-by: Jussi Kukkonen <jku@goto.fi>
Signed-off-by: Lukas Pühringer <luk.puehringer@gmail.com>

Author: lukpueh

tuf/ngclient/_internal/trusted_metadata_set.py

@@ -401,7 +401,7 @@ def update_delegated_targets(
         # does not match meta version in timestamp
         self._check_final_snapshot()
 
-        delegator: Optional[Union[Root, Targets]] = self.get(delegator_name)
+        delegator: Optional[Delegator] = self.get(delegator_name)
         if delegator is None:
             raise RuntimeError("Cannot load targets before delegator")