Ignore typing warning (stdout should always exist)

If stdout doesn't exist (is None) then the the files wouldn't even be
received.

dangerzone/isolation_provider/qubes.py

@@ -136,7 +136,7 @@ def _convert(
                 self.print_progress_trusted(document, False, text, percentage)
 
         # Ensure nothing else is read after all bitmaps are obtained
-        p.stdout.close()
+        p.stdout.close()  # typing: ignore [union-attr]
 
         # TODO handle leftover code input
         text = "Converted document to pixels"