Async side-effect focused repeater is broken

[adam-rocska]

This test fails miserably:

func testRepeatingAsync_sideEffectFocused() async throws {
  actor Counter {
    var count = 0
    func increment() { count += 1 }
  }
  let counter = Counter()
  await repeating(count: 13, await counter.increment())
  let result = await counter.count
  XCTAssertEqual(result, 13)
}