macOS: Fix issue with not being able to add favorites for existing bo…

…okmarks in the latest 1.70.0 internal (#2059)

Task/Issue URL: https://app.asana.com/0/0/1206339303679760/f

Description
This is broken only on our internals.
If a bookmark exists, the user cannot add it as a favorite through the "Add favorite" option in the home page.

DuckDuckGo/Bookmarks/ViewModel/AddBookmarkModalViewModel.swift

@@ -54,7 +54,7 @@ struct AddBookmarkModalViewModel {
         }
 
         var result: Bookmark?
-        if var bookmark = originalBookmark {
+        if var bookmark = originalBookmark ?? bookmarkManager.getBookmark(for: url) {
 
             if url.absoluteString != bookmark.url {
                 bookmark = bookmarkManager.updateUrl(of: bookmark, to: url) ?? bookmark