fix output type for actors without interests

racket/typed/core-types.rkt

@@ -675,6 +675,9 @@
     [(~Message τ)
      (define t (replace-bind-and-discard-with-★ #'τ))
      (type-eval #`(Observe #,t))]
+    [τ
+     #:when (bot? #'τ)
+     #'τ]
     [τ
      (define t (replace-bind-and-discard-with-★ #'τ))
      (type-eval #`(Observe #,t))]))