GHSA-vr26-jcq5-fjj8

### Summary

As of quinn-proto 0.11, it is possible for a server to `accept()`, `retry()`, `refuse()`, or `ignore()` an `Incoming` connection. However, calling `retry()` on an unvalidated connection exposes the server to a likely panic in the following situations:

- Calling `refuse` or `ignore` on the resulting validated connection, if a duplicate initial packet is received - This issue can go undetected until a server's `refuse()`/`ignore()` code path is exercised, such as to stop a denial of service attack. - Accepting when the initial packet for the resulting validated connection fails to decrypt or exhausts connection IDs, if a similar initial packet that successfully decrypts and doesn't exhaust connection IDs is received. - This issue can go undetected if clients are well-behaved.

The former situation was observed in a real application, while the latter is only theoretical.

### Details

Location of panic: https://github.com/quinn-rs/quinn/blob/bb02a12a8435a7732a1d762783eeacbb7e50418e/quinn-proto/src/endpoint.rs#L213

### Impact Denial of service for internet-facing server