Fix mypy stub enum compatibility

without losing numeric semantics

stubs/mpd/base.pyi

@@ -1,18 +1,18 @@
-from enum import Enum
+from enum import IntEnum
 
-class FailureResponseCode(Enum):
-    NOT_LIST: int
-    ARG: int
-    PASSWORD: int
-    PERMISSION: int
-    UNKNOWN: int
-    NO_EXIST: int
-    PLAYLIST_MAX: int
-    SYSTEM: int
-    PLAYLIST_LOAD: int
-    UPDATE_ALREADY: int
-    PLAYER_SYNC: int
-    EXIST: int
+class FailureResponseCode(IntEnum):
+    NOT_LIST = ...
+    ARG = ...
+    PASSWORD = ...
+    PERMISSION = ...
+    UNKNOWN = ...
+    NO_EXIST = ...
+    PLAYLIST_MAX = ...
+    SYSTEM = ...
+    PLAYLIST_LOAD = ...
+    UPDATE_ALREADY = ...
+    PLAYER_SYNC = ...
+    EXIST = ...
 
 class MPDError(Exception): ...