SQ: Fix missing GenericAlias in Python 3.8

trycast.py

@@ -11,7 +11,7 @@
 from collections.abc import MutableSequence as CMutableSequence
 from collections.abc import Sequence as CSequence
 from inspect import Parameter
-from types import GenericAlias, ModuleType
+from types import ModuleType
 from typing import ForwardRef  # type: ignore[import-error]  # pytype (for ForwardRef)
 from typing import _GenericAlias  # type: ignore[attr-defined]
 from typing import (
@@ -40,10 +40,22 @@
 from typing import _type_repr as type_repr  # type: ignore[attr-defined]
 from typing import cast, get_args, get_origin, overload
 
+
+# GenericAlias
+if sys.version_info >= (3, 9):
+    from types import GenericAlias
+else:
+
+    class GenericAlias(type):  # type: ignore[no-redef]
+        def __init__(self, origin: object, args: tuple[object, ...]) -> None: ...
+
+        ...
+
+
 # UnionType
-try:
+if sys.version_info >= (3, 10):
     from types import UnionType  # type: ignore[attr-defined]
-except ImportError:
+else:
 
     class UnionType(type):  # type: ignore[no-redef]
         ...