Fix context types

Author: srittau

asserts/__init__.pyi

@@ -28,9 +28,9 @@ class AssertRaisesContext(Generic[_E]):
     def __enter__(self: _S) -> _S: ...
     def __exit__(
         self, exc_type: Optional[Type[BaseException]], exc_val: Optional[BaseException], exc_tb: Optional[TracebackType]
-    ) -> Optional[bool]: ...
+    ) -> bool: ...
     def format_message(self, default_msg: Text) -> Text: ...
-    def add_test(self, cb: Callable[[_E], None]) -> None: ...
+    def add_test(self, cb: Callable[[_E], Any]) -> None: ...
 
 class AssertRaisesErrnoContext(AssertRaisesContext[_E]):
     expected_errno: int
@@ -43,9 +43,11 @@ class AssertRaisesRegexContext(AssertRaisesContext[_E]):
 class AssertWarnsContext:
     def __init__(self, warning_class: Type[Warning], msg_fmt: Text = ...) -> None: ...
     def __enter__(self: _S) -> _S: ...
-    def __exit__(self, exc_type: Type[BaseException], exc_val: BaseException, exc_tb: Any) -> None: ...
+    def __exit__(
+        self, exc_type: Optional[Type[BaseException]], exc_val: Optional[BaseException], exc_tb: Optional[TracebackType],
+    ) -> None: ...
     def format_message(self) -> Text: ...
-    def add_test(self, cb: Callable[[Warning], None]) -> None: ...
+    def add_test(self, cb: Callable[[Warning], bool]) -> None: ...
 
 class AssertWarnsRegexContext(AssertWarnsContext):
     pattern: Text