ignore `@proxy` in strong mode

pkg/dev_compiler/test/not_yet_strong_tests.dart

 import 'dart:collection';
 import 'package:path/path.dart' as path;
 
 /// The set of tests that are not yet strong mode safe.
 final notYetStrongTests = new HashSet<String>.from([
   'language/abstract_exact_selector_test_01_multi',
   'language/abstract_factory_constructor_test_00_multi',
   'language/abstract_getter_test_01_multi',
   'language/abstract_runtime_error_test_01_multi',
   'language/abstract_runtime_error_test_02_multi',
@@ skipping 1406 matching lines @@
   'language/private_access_test_02_multi',
   'language/private_access_test_03_multi',
   'language/private_access_test_04_multi',
   'language/private_access_test_05_multi',
   'language/private_access_test_06_multi',
   'language/private_mixin2_test',
   'language/private_test',
   'language/propagated_argument_type_check_test',
   'language/property_field_override_test',
   'language/proxy2_test_01_multi',
+  'language/proxy2_test_03_multi',
+  'language/proxy2_test_04_multi',
   'language/proxy2_test_02_multi',
   'language/proxy3_test_01_multi',
   'language/proxy3_test_02_multi',
   'language/proxy3_test_03_multi',
   'language/proxy3_test_04_multi',
   'language/proxy_test_01_multi',
   'language/proxy_test_02_multi',
+  'language/proxy_test_03_multi',
+  'language/proxy_test_04_multi',
   'language/proxy_test_05_multi',
   'language/proxy_test_06_multi',
   'language/redirecting_constructor_initializer_test',
   'language/redirecting_factory_default_values_test_01_multi',
   'language/redirecting_factory_default_values_test_02_multi',
   'language/redirecting_factory_default_values_test_none_multi',
   'language/redirecting_factory_incompatible_signature_test',
   'language/redirecting_factory_infinite_steps_test_01_multi',
   'language/redirecting_factory_infinite_steps_test_02_multi',
   'language/redirecting_factory_long_test',
@@ skipping 967 matching lines @@
   'lib/html/mutationobserver_test',
   'lib/html/postmessage_structured_test',
   'lib/html/resource_http_test',
   'lib/html/transferables_test',
   'lib/html/webgl_1_test',
   'lib/html/wrapping_collections_test',
   // TODO(jmesserly): these are both under "dart:html" as well.
   'js_test',
   'js_util_test'
 ].map((p) => p.replaceAll('/', path.separator)));