Fix Literal for older version

src/_pytest/tmpdir.py

@@ -13,6 +13,8 @@ from typing import Union
 if TYPE_CHECKING:
     from typing_extensions import Literal
 
+    RetentionType = Literal["all", "failed", "none"]
+
 
 import attr
 from _pytest.config.argparsing import Parser
@@ -45,13 +47,13 @@ class TempPathFactory:
     _trace = attr.ib()
     _basetemp = attr.ib(type=Optional[Path])
     _retention_count = attr.ib(type=int)
-    _retention_policy = attr.ib(type=RetentionPolicy)
+    _retention_policy = attr.ib(type="RetentionType")
 
     def __init__(
         self,
         given_basetemp: Optional[Path],
         retention_count: int,
-        retention_policy: RetentionPolicy,
+        retention_policy: "RetentionType",
         trace,
         basetemp: Optional[Path] = None,
         *,