fix(CatalogVerifier): relax typing < Python 3.9

When typing[1] exc_type as Optional[type[BaseException]], there seems to
be no way around "TypeError: 'type' object is not subscriptable" in our
current Python 3.8, even using __future__.annotations.

[1]: https://adamj.eu/tech/2021/07/04/python-type-hints-how-to-type-a-context-manager/

devops/scripts/verify-mo.py

@@ -20,10 +20,8 @@
 import os
 import shlex
 import subprocess
-from collections.abc import Iterator
 from pathlib import Path
-from types import TracebackType
-from typing import Optional, Set
+from typing import Any, Iterator, Optional, Set
 
 import polib
 from translate.tools.pocompile import convertmo
@@ -61,9 +59,9 @@ def __enter__(self) -> "CatalogVerifier":
 
     def __exit__(
         self,
-        exc_type: Optional[type[BaseException]],
-        exc_value: Optional[BaseException],
-        traceback: Optional[TracebackType],
+        exc_type: Optional[Any],
+        exc_value: Optional[Any],
+        traceback: Optional[Any],
     ) -> None:
         """Clean up."""