collections: fix some Counter nits (#7313)

Author: hauntsaninja

stdlib/collections/__init__.pyi

@@ -277,9 +277,12 @@ class Counter(dict[_T, int], Generic[_T]):
     def update(self, __m: Iterable[_T] | Iterable[tuple[_T, int]], **kwargs: int) -> None: ...
     @overload
     def update(self, __m: None = ..., **kwargs: int) -> None: ...
+    def __missing__(self, key: _T) -> int: ...
     def __delitem__(self, elem: object) -> None: ...
-    def __eq__(self, other: object) -> bool: ...
-    def __ne__(self, other: object) -> bool: ...
+    if sys.version_info >= (3, 10):
+        def __eq__(self, other: object) -> bool: ...
+        def __ne__(self, other: object) -> bool: ...
+
     def __add__(self, other: Counter[_T]) -> Counter[_T]: ...
     def __sub__(self, other: Counter[_T]) -> Counter[_T]: ...
     def __and__(self, other: Counter[_T]) -> Counter[_T]: ...