Account for Python 3.9 when defining unions

The union for _Match is not defined as part of a function annotation, so
the "annotations" import from __future__ does not take effect and thus
results in a syntax error on Python < 3.10. To fix, the Union
annotation is used for this one type definition.

path/__init__.py

@@ -72,7 +72,7 @@
 )
 
 if TYPE_CHECKING:
-    from typing_extensions import Literal, Never, Self
+    from typing_extensions import Literal, Never, Self, Union
     from _typeshed import (
         OpenBinaryMode,
         OpenBinaryModeReading,
@@ -82,7 +82,7 @@
         ExcInfo,
     )
 
-    _Match = str | Callable[[str], bool] | None
+    _Match = Union[str, Callable[[str], bool], None]
     _CopyFn = Callable[[str, str], object]
     _IgnoreFn = Callable[[str, list[str]], Iterable[str]]
     _OnErrorCallback = Callable[[Callable[..., Any], str, ExcInfo], object]