[Bug]:A potential goroutine leak

Hello @samuelkarp, When I used fifo, I found a potential bug, I'm not sure, maybe we can discuss to avoid a goleak
blocking position:
https://github.com/containerd/fifo/blob/3e17f98903a83f1a6c7368ea4694e6861161d6bd/fifo.go#L124-L133
if users use the OpenFilo() with the parameters like this:
`f, err := OpenFifo(context.Background(), filepath.Join(tmpdir, "f0"), syscall.O_RDONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0600)`
The select statement will block beacuse there is no cancelFunc to awaken the <-ctx.Done().

I wrote a test function to reproduce the bug considering the test that https://github.com/containerd/fifo/blob/3e17f98903a83f1a6c7368ea4694e6861161d6bd/fifo_test.go#L47

```
func TestFifoNocancel(t *testing.T) {
defer goleak.VerifyNone(t)
tmpdir, err := os.MkdirTemp("", "fifos")
assert.NoError(t, err)
defer os.RemoveAll(tmpdir)

leakCheckWg = &sync.WaitGroup{}
defer func() {
leakCheckWg = nil
}()

//f, err := OpenFifo(context.Background(), filepath.Join(tmpdir, "f0"), syscall.O_RDONLY|syscall.O_NONBLOCK, 0600)
f, err := OpenFifo(context.Background(), filepath.Join(tmpdir, "f0"), syscall.O_RDONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0600)
assert.Exactly(t, nil, f)
assert.NotNil(t, err)
assert.NoError(t, checkWgDone(leakCheckWg))
}
```
The test result shows it is a goroutine leak, you can use goleak to reproduce the bug.