Import Iterable and Iterator depending on Python version

libkeyringctl/{keyring,sequoia,util}.py:
As Iterable and Iterator are only used for type hints, switch to using
typing.{Iterable,Iterator} instead of
collections.abc.{Iterable,Iterator} for Python < 3.9.0, as older Python
interpreters will otherwise raise TypeError.

libkeyringctl/sequoia.py

@@ -1,12 +1,18 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 
-from collections.abc import Iterable
 from datetime import datetime
 from functools import reduce
 from pathlib import Path
+from platform import python_version_tuple
 from re import sub
 from tempfile import mkdtemp
 from typing import Dict
+
+# NOTE: remove after python 3.8.x is no longer supported upstream
+if int(python_version_tuple()[1]) < 9:  # pragma: no cover
+    from typing import Iterable
+else:
+    from collections.abc import Iterable
 from typing import List
 from typing import Optional