Define trio.Event.__bool__() to reduce bugs

Closes #3238

Author: CoolCat467

src/trio/_sync.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 import math
-from typing import TYPE_CHECKING, Protocol
+from typing import TYPE_CHECKING, NoReturn, Protocol
 
 import attrs
 
@@ -112,6 +112,14 @@ def statistics(self) -> EventStatistics:
         """
         return EventStatistics(tasks_waiting=len(self._tasks))
 
+    if not TYPE_CHECKING:
+
+        def __bool__(self) -> NoReturn:
+            """Raise NotImplementedError."""
+            raise NotImplementedError(
+                "Trio events cannot be treated as bools; consider using 'event.is_set()'"
+            )
+
 
 class _HasAcquireRelease(Protocol):
     """Only classes with acquire() and release() can use the mixin's implementations."""