Fix counter display number incorrectly displayed on the page (#29448) (#29478)

Backport #29448 by @charles7668

issue : #28239

The counter number script uses the 'checkbox' attribute to determine
whether an item is selected or not.

However, the input event only increments the counter value, and when
more items are displayed, it does not update all previously loaded
items.

As a result, the display becomes incorrect because it triggers the
update counter script, but checkboxes that are selected without the
'checked' attribute are not counted

Co-authored-by: charles <30816317+charles7668@users.noreply.github.com>

web_src/js/features/pull-view-file.js

@@ -44,9 +44,11 @@ export function initViewedCheckboxListenerFor() {
       // Mark the file as viewed visually - will especially change the background
       if (this.checked) {
         form.classList.add(viewedStyleClass);
+        checkbox.setAttribute('checked', '');
         prReview.numberOfViewedFiles++;
       } else {
         form.classList.remove(viewedStyleClass);
+        checkbox.removeAttribute('checked');
         prReview.numberOfViewedFiles--;
       }