[3.10] bpo-44559: [Enum] revert enum module to 3.9 (GH-27010)

* [Enum] revert enum module to 3.9
diff --git a/Lib/inspect.py b/Lib/inspect.py
index 9f8cc01..0273ffa 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -2561,6 +2561,9 @@ class _ParameterKind(enum.IntEnum):
     KEYWORD_ONLY = 3
     VAR_KEYWORD = 4
 
+    def __str__(self):
+        return self._name_
+
     @property
     def description(self):
         return _PARAM_NAME_MAPPING[self]