Fix flakey tests

Author: stephencelis

Sources/ComposableArchitecture/TestStore.swift

@@ -265,7 +265,9 @@
 
           switch effects.operation {
           case .none:
+            self.effectDidSubscribe.continuation.yield()
             return .none
+
           case .publisher, .run:
             let effect = LongLivingEffect(file: action.file, line: action.line)
             return