`sync::mpsc::select::test::stress` is flaky on Windows

Using Rust rev dcc6ce2c772cb851ac35cbc2ddafcae9bf2fa9fd, stage1 stdtest.

```
$ ./stdtest-x86_64-pc-windows-gnu.exe sync::mpsc::select::test::

thread '<unnamed>' panicked at 'assertion failed: i % 2 == 1 && i == i2.unwrap()',
C:\home\stone\rust\src\libstd\sync\mpsc\select.rs:493

test sync::mpsc::select::test::stress ... FAILED
```

cc #22628, #22710
