QSslSocket::setCiphers() documentation uses weak cyphers

The code snippet documenting the use of QSslSocket::::setCiphers() makes use of three ciphers considered weak, see e.g. https://ciphersuite.info/cs/TLS_DHE_DSS_WITH_AES_256_CBC_SHA/. To avoid copy/paste mistakes or cargoculting, it might be better to show the use of some stronger ciphers instead.