FeignException could not be serialized if cause class is UnknowHostException

feign 10.12, 11.5.
FeignException serialization produces error when cause class is UnknowHostException.
How to reproduce:

    @Test
    public void testFeignSerialization() throws IOException {
        try {
            SomeApi target = new Feign.Builder()
                    .target(SomeApi.class, "https://some-non-existing-host-for-unit-test");
            target.ping(); 
        } catch (RetryableException e) {
            try (ByteArrayOutputStream bos = new ByteArrayOutputStream();
                 ObjectOutputStream out = new ObjectOutputStream(bos)) {
                out.writeObject(e);
                byte[] serialized = bos.toByteArray();
            }
        }
    }

    public interface SomeApi {
        @RequestLine("GET /ping")
        void ping();
    }

This code fails trying serialize Target$HardCodedTarget instance in e.request.requestTemplate.feignTarget.

I see in RequestTemplate that it implements Serializable, but Target (field feignTarget) implementations are not Serializable.
Also UriTemplate (field uriTemplate) is not Seralizable too.

Start with RequestTemplate and inspect its feignTarget and uriTemplate fields, especially Target$HardCodedTarget and UriTemplate, which the report identifies as serialization failures. Reproduce the provided test with ObjectOutputStream and add a regression test around FeignException serialization. Done means the reproduced exception can be serialized successfully.