Always use bool and Literal for Python compat code (#9213)

stubs/requests/requests/compat.pyi

@@ -1,6 +1,6 @@
 from builtins import bytes as bytes, str as str
 from collections import OrderedDict as OrderedDict
-from typing_extensions import TypeAlias
+from typing_extensions import Literal, TypeAlias
 from urllib.parse import (
     quote as quote,
     quote_plus as quote_plus,
@@ -15,8 +15,8 @@ from urllib.parse import (
 )
 from urllib.request import getproxies as getproxies, parse_http_list as parse_http_list, proxy_bypass as proxy_bypass
 
-is_py2: bool
-is_py3: bool
+is_py2: Literal[False]
+is_py3: Literal[True]
 has_simplejson: bool
 
 builtin_str: TypeAlias = str  # noqa: Y042