Close http3 roundtripper when error occurred

For http3, if the network were down, the quic transport needs to be
closed, so the transport can create new connection when network up.

doh.go

@@ -48,6 +48,9 @@ func (r *dohResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, erro
 	}
 	resp, err := c.Do(req)
 	if err != nil {
+		if r.isDoH3 {
+			r.http3RoundTripper.Close()
+		}
 		return nil, fmt.Errorf("could not perform request: %w", err)
 	}
 	defer resp.Body.Close()