fix: consider OIDC registration flows errored with duplicate credenti…

…al to be completed by strategy (#3525)

Returning anything else here may cause Kratos to respond with two concatenated JSON objects: new login flow with actual error message as the first one and a very confusing '500, aborted registration hook execution' as the second one.

selfservice/strategy/oidc/strategy.go

@@ -552,7 +552,7 @@ func (s *Strategy) handleError(w http.ResponseWriter, r *http.Request, f flow.Fl
 			// return a new login flow with the error message embedded in the login flow.
 			x.AcceptToRedirectOrJSON(w, r, s.d.Writer(), lf, lf.AppendTo(s.d.Config().SelfServiceFlowLoginUI(r.Context())).String())
 			// ensure the function does not continue to execute
-			return registration.ErrHookAbortFlow
+			return flow.ErrCompletedByStrategy
 		}
 
 		rf.UI.Nodes = node.Nodes{}