Corrected (Base)ExceptionGroup names and types (#6895)

The second argument to `ExceptionGroup` is positional-only. The `exceptions` property always returns a tuple, no matter what the type of the original `__exceptions` argument is.

Author: agronholm

stdlib/builtins.pyi

@@ -1670,11 +1670,11 @@ if sys.version_info >= (3, 11):
         @property
         def message(self) -> str: ...
         @property
-        def exceptions(self) -> Sequence[BaseException]: ...
+        def exceptions(self) -> tuple[BaseException, ...]: ...
         def subgroup(self: Self, __condition: _SplitCondition) -> Self | None: ...
         def split(self: Self, __condition: _SplitCondition) -> tuple[Self | None, Self | None]: ...
         def derive(self: Self, __excs: Sequence[BaseException]) -> Self: ...
     class ExceptionGroup(BaseExceptionGroup, Exception):
-        def __new__(cls, __message: str, exceptions: Sequence[Exception]) -> ExceptionGroup: ...
+        def __new__(cls, __message: str, __exceptions: Sequence[Exception]) -> ExceptionGroup: ...
         @property
-        def exceptions(self) -> Sequence[Exception]: ...
+        def exceptions(self) -> tuple[Exception, ...]: ...