[mob][photos] Lint suggestions

mobile/lib/ui/cast/auto.dart

@@ -56,7 +56,7 @@ class _AutoCastDialogState extends State<AutoCastDialog> {
               }
 
               if (snapshot.data!.isEmpty) {
-                return const Center(child: Text(S.of(context).noDeviceFound));
+                return Center(child: Text(S.of(context).noDeviceFound));
               }
 
               return Column(

mobile/lib/ui/cast/choose.dart

@@ -6,9 +6,9 @@ import "package:photos/ui/components/buttons/button_widget.dart";
 import "package:photos/ui/components/models/button_type.dart";
 
 class CastChooseDialog extends StatefulWidget {
-  CastChooseDialog({
+  const CastChooseDialog({
     Key? key,
-  }) : super(key: key) {}
+  }) : super(key: key);
 
   @override
   State<CastChooseDialog> createState() => _CastChooseDialogState();

mobile/lib/ui/viewer/gallery/gallery_app_bar_widget.dart

@@ -861,7 +861,7 @@ class _GalleryAppBarWidgetState extends State<GalleryAppBarWidget> {
       context: context,
       barrierDismissible: true,
       builder: (BuildContext context) {
-        return CastChooseDialog();
+        return const CastChooseDialog();
       },
     );
     _logger.info("Cast result: $result");