Fix #28120, strong mode allows field overrides

pkg/analyzer/test/generated/compile_time_error_code_test.dart

Index: pkg/analyzer/test/generated/compile_time_error_code_test.dart
diff --git a/pkg/analyzer/test/generated/compile_time_error_code_test.dart b/pkg/analyzer/test/generated/compile_time_error_code_test.dart
index e8f7e11f19e915afe08ea9160608a8c5e050f691..8fc72fab1aa25743af82e243262118a506770a7d 100644
--- a/pkg/analyzer/test/generated/compile_time_error_code_test.dart
+++ b/pkg/analyzer/test/generated/compile_time_error_code_test.dart
@@ -5291,10 +5291,8 @@ import 'lib1.dart';
 class C extends Object with A, B {}
 ''');
     await computeAnalysisResult(source);
-    assertErrors(source, [
-      CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION,
-      StrongModeCode.INVALID_FIELD_OVERRIDE
-    ]);
+    assertErrors(
+        source, [CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION]);
     verify([source]);
   }
 
@@ -5340,10 +5338,8 @@ import 'lib1.dart';
 class C extends A with B {}
 ''');
     await computeAnalysisResult(source);
-    assertErrors(source, [
-      CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION,
-      StrongModeCode.INVALID_FIELD_OVERRIDE
-    ]);
+    assertErrors(
+        source, [CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION]);
     verify([source]);
   }
 
@@ -5365,10 +5361,8 @@ import 'lib1.dart';
 class C extends A with A {}
 ''');
     await computeAnalysisResult(source);
-    assertErrors(source, [
-      CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION,
-      StrongModeCode.INVALID_FIELD_OVERRIDE
-    ]);
+    assertErrors(
+        source, [CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION]);
     verify([source]);
   }