Change TypeAlias for Python 3.9

Author: ptr-yudai

ptrlib/types/enums.py

@@ -1,4 +1,5 @@
-from typing import Literal, TypeAlias, Union, SupportsInt, SupportsIndex
+from typing_extensions import TypeAlias
+from typing import Literal, Union, SupportsInt, SupportsIndex
 
 PtrlibArchT = Literal['unknown', 'intel', 'arm', 'risc-v', 'sparc', 'mips']
 PtrlibBitsT = Literal[16, 32, 64]