remove field override, assign to super field instead (#135165)

Removes an ignore about overriding fields. Instead we just assign the value to the original field in the super class.

Related to dart-lang/language#3332 (discovered during investigations into the violation of that lint).

packages/flutter_tools/test/commands.shard/hermetic/run_test.dart

@@ -1335,13 +1335,10 @@ class FakeIOSDevice extends Fake implements IOSDevice {
 
 class TestRunCommandForUsageValues extends RunCommand {
   TestRunCommandForUsageValues({
-   this.devices,
-  });
-
-  @override
-  // devices is not set within usageValues, so we override the field
-  // ignore: overridden_fields
-  List<Device>? devices;
+    List<Device>? devices,
+  }) {
+    this.devices = devices;
+  }
 
   @override
   Future<BuildInfo> getBuildInfo({ BuildMode? forcedBuildMode, File? forcedTargetFile }) async {