`FastFallbackTest.preferCallConnectionOverDeferredConnection` flaky

On 'jvm(21)' runner:

```
FastFallbackTest[jvm] > preferCallConnectionOverDeferredConnection()[jvm] FAILED
    org.opentest4j.AssertionFailedError: expected:<"[this was the 2nd request on IPv4]"> but was:<"[unexpected call to IPv6]">
        at app//okhttp3.FastFallbackTest.preferCallConnectionOverDeferredConnection(FastFallbackTest.kt:330)
```