Don't insert additional ':' when changing a named argument name.

pkg/analysis_server/test/domain_completion_test.dart

Index: pkg/analysis_server/test/domain_completion_test.dart
diff --git a/pkg/analysis_server/test/domain_completion_test.dart b/pkg/analysis_server/test/domain_completion_test.dart
index ec7c5205e4ec0d4d8dfd159b3c4ee6f155575d4b..81d8a353ac3b79acc58eda76eefa37231b298c33 100644
--- a/pkg/analysis_server/test/domain_completion_test.dart
+++ b/pkg/analysis_server/test/domain_completion_test.dart
@@ -51,9 +51,9 @@ class CompletionDomainHandlerTest extends AbstractCompletionDomainTest {
   test_ArgumentList_imported_function_named_param_label1() async {
     addTestFile('main() { int.parse("16", r^: 16);}');
     await getSuggestions();
-    assertHasResult(CompletionSuggestionKind.NAMED_ARGUMENT, 'radix: ',
+    assertHasResult(CompletionSuggestionKind.NAMED_ARGUMENT, 'radix',
         relevance: DART_RELEVANCE_NAMED_PARAMETER);
-    assertHasResult(CompletionSuggestionKind.NAMED_ARGUMENT, 'onError: ',
+    assertHasResult(CompletionSuggestionKind.NAMED_ARGUMENT, 'onError',
         relevance: DART_RELEVANCE_NAMED_PARAMETER);
     expect(suggestions, hasLength(2));
   }