Update NumberFactModelTests.swift (#146)

Line missing from committed sample that is in the transcript of the video and which seems to be necessary in Xcode 17beta6 to make this test pass.

0242-reliably-testing-async-pt5/ReliablyTestingAsync/ReliablyTestingAsyncTests/NumberFactModelTests.swift

@@ -149,6 +149,7 @@ final class NumberFactModelTests: XCTestCase {
     model.getFactButtonTapped()
     XCTAssertEqual(model.isLoading, true)
     fact.send("0 is a good number.")
+    fact.send(completion: .finished)
     XCTAssertEqual(model.fact, "0 is a good number.")
     XCTAssertEqual(model.isLoading, false)
   }