[UI-Kit] Disable attachment download dialog pop using back button

Signed-off-by: Sahil Kumar <[email protected]>

packages/stream_chat_flutter/lib/src/attachment_actions_modal.dart

@@ -207,7 +207,9 @@ class AttachmentActionsModal extends StatelessWidget {
     ValueNotifier<_DownloadProgress> progressNotifier,
   ) {
     final theme = StreamChatTheme.of(context);
-    return ValueListenableBuilder(
+    return WillPopScope(
+      onWillPop: () => Future.value(false),
+      child: ValueListenableBuilder(
         valueListenable: progressNotifier,
         builder: (_, _DownloadProgress progress, __) {
           final value = progress.toProgressIndicatorValue;
@@ -266,6 +268,7 @@ class AttachmentActionsModal extends StatelessWidget {
             ),
           );
         },
+      ),
     );
   }