[mob][photos] Migrate use of WillPopScope to PopScope (#1473)

## Description

[Documentation followed for the
migration](https://docs.flutter.dev/release/breaking-changes/android-predictive-back)

## Tests

- [x] Tested screens in which migration wasn't straight forward
(HomeScreen)

mobile/lib/ui/common/linear_progress_dialog.dart

@@ -27,8 +27,8 @@ class LinearProgressDialogState extends State<LinearProgressDialog> {
 
   @override
   Widget build(BuildContext context) {
-    return WillPopScope(
-      onWillPop: () async => false,
+    return PopScope(
+      canPop: false,
       child: AlertDialog(
         title: Text(
           widget.message,