typing: disable [unsupported-operands] warning in the largefiles outgoing hook

For some reason, pytype thinks `toupload` is a set:

    No attribute '__setitem__' on Set[nothing]

(It actually is a set in the subsequent `else` branch, but I'm not interested in
trying to rewrite this to be consistent.)

hgext/largefiles/overrides.py

@@ -1436,7 +1436,7 b' def outgoinghook(ui, repo, other, opts, '
 
             def addfunc(fn, lfhash):
                 if fn not in toupload:
-                    toupload[fn] = []
+                    toupload[fn] = []  # pytype: disable=unsupported-operands
                 toupload[fn].append(lfhash)
                 lfhashes.add(lfhash)