electrum protocol: add support for 1.6, but keep supporting 1.4 - #10295

✅ 00:18 clone
✅ 00:01 pip
✅ 00:01 bitcoind
✅ 00:43 install
✅ 00:01 libsecp_build
✅ 00:00 bitcoind_service
✅ 00:00 electrumx_service
✅ 17:25 regtest
✔️ 00:00 wallet
✅ 00:00 Upload 'pip' cache
✅ 00:00 Upload 'bitcoind' cache
✅ 00:00 Upload 'libsecp_build' cache