Fix import errors in Python 3.9

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## v1.3.0 (unreleased)
 
 - Added support for `.header.yml` config files.
+- Fixed compatibility with Python 3.9.
 
 ## v1.2.0
 

src/unbeheader/typing.py

@@ -6,10 +6,10 @@
 from re import Pattern
 from typing import Any
 from typing import NamedTuple
-from typing import TypeAlias
 
-ConfigDict: TypeAlias = dict[str, Any]
-PathCache: TypeAlias = dict[Path, bool]
+# TODO: Use explicit TypeAlias when Python 3.9 is dropped
+ConfigDict = dict[str, Any]
+PathCache = dict[Path, bool]
 
 
 @dataclass

src/unbeheader/util.py

@@ -1,6 +1,8 @@
 # This file is part of Unbeheader.
 # Copyright (C) CERN & UNCONVENTIONAL
 
+from __future__ import annotations
+
 import re
 from pathlib import Path
 from re import Match