Apply suggestions from code review

Author: A5rocks

newsfragments/3322.deprecated.txt

@@ -1 +1 @@
-Implement `trio.Event.__bool__` and have it raise a `DeprecationWarning` and tell users to use `trio.Event.is_set` instead. Would be caught earlier with `mypy --enable-error-code=truthy-bool`, this is for users who don't use mypy.
+Implement ``bool(trio.Event)`` and have it raise a `DeprecationWarning` and tell users to use `trio.Event.is_set` instead. This is an alternative to ``mypy --enable-error-code=truthy-bool`` for users who don't use type checking.

src/trio/_sync.py

@@ -113,7 +113,7 @@ def statistics(self) -> EventStatistics:
         """
         return EventStatistics(tasks_waiting=len(self._tasks))
 
-    def __bool__(self) -> True:
+    def __bool__(self) -> Literal[True]:
         """Return True and raise warning."""
         warn_deprecated(
             self.__bool__,