un-inline ki protection decorator

new f_locals method doesn't create a cycle in this situation

src/trio/_core/_run.py

@@ -623,6 +623,7 @@ def _close(self, exc: BaseException | None) -> BaseException | None:
             self._cancel_status = None
         return exc
 
+    @enable_ki_protection
     def __exit__(
         self,
         etype: type[BaseException] | None,
@@ -633,10 +634,6 @@ def __exit__(
         # so __exit__() must be just _close() plus this logic for adapting
         # the exception-filtering result to the context manager API.
 
-        # This inlines the enable_ki_protection decorator so we can fix
-        # f_locals *locally* below to avoid reference cycles
-        sys._getframe().f_locals[LOCALS_KEY_KI_PROTECTION_ENABLED] = True
-
         # Tracebacks show the 'raise' line below out of context, so let's give
         # this variable a name that makes sense out of context.
         remaining_error_after_cancel_scope = self._close(exc)