fix NSM error when completing imported inherited private fields

pkg/analysis_server/test/services/completion/imported_computer_test.dart

Index: pkg/analysis_server/test/services/completion/imported_computer_test.dart
diff --git a/pkg/analysis_server/test/services/completion/imported_computer_test.dart b/pkg/analysis_server/test/services/completion/imported_computer_test.dart
index fd323e2b5b9704f1e5d350c582fcd2bfc697589c..6f0088b75491846b25714a3d36faae0ed003b488 100644
--- a/pkg/analysis_server/test/services/completion/imported_computer_test.dart
+++ b/pkg/analysis_server/test/services/completion/imported_computer_test.dart
@@ -221,6 +221,7 @@ class ImportedComputerTest extends AbstractSelectorSuggestionTest {
       assertNotCached('e1');
       assertNotCached('i2');
       assertNotCached('m1');
+      assertNotCached('_pf');
     });
   }