updater: workaround CPython bug 128211

Python 3.13 list comprehensions are buggy [1]: [i for i in x] calls
iter(iter(x)) instead of just iter(x).  Work around the bug by having
UpdateListIter have a __iter__(self) that just returns self.  This is
the same thing that the standard library does:

    x = iter([])
    print(x is iter(x))

prints True.

[1]: python/cpython#128211

qui/updater/utils.py

@@ -264,6 +264,9 @@ def __init__(self, list_store_wrapped):
         self.list_store_wrapped = list_store_wrapped
         self._id = -1
 
+    def __iter__(self) -> 'UpdateListIter':
+        return self
+
     def __next__(self) -> RowWrapper:
         self._id += 1
         if 0 <= self._id < len(self.list_store_wrapped):