Public EC key from buffer

In net-ssh, there is following code:

        public_key_oct = buffer.read_string
        begin
          key = OpenSSL::PKey::EC.new(OpenSSL::PKey::EC::CurveNameAlias[curve_name_in_key])
          group = key.group
          point = OpenSSL::PKey::EC::Point.new(group, OpenSSL::BN.new(public_key_oct, 2))
          key.public_key = point

          return key
        rescue OpenSSL::PKey::ECError
          raise NotImplementedError, "unsupported key type `#{type}'"
        end

Which fails with OpenSSL 3.x:

  1) Error:
Transport::Kex::TestEcdhSHA2NistP256#test_exchange_keys_should_return_expected_results_when_successful:
OpenSSL::PKey::PKeyError: pkeys are immutable on OpenSSL 3.0
    /builddir/net-ssh/lib/net/ssh/transport/openssl.rb:164:in `public_key='
    /builddir/net-ssh/lib/net/ssh/transport/openssl.rb:164:in `read_keyblob'
    /builddir/net-ssh/lib/net/ssh/buffer.rb:325:in `read_keyblob'
    /builddir/net-ssh/lib/net/ssh/buffer.rb:248:in `read_key'
    /builddir/net-ssh/lib/net/ssh/transport/kex/abstract5656.rb:54:in `send_kexinit'
    /builddir/net-ssh/lib/net/ssh/transport/kex/abstract.rb:48:in `exchange_keys'
    /builddir/net-ssh/test/transport/kex/test_ecdh_sha2_nistp256.rb:96:in `exchange!'
    /builddir/net-ssh/test/transport/kex/test_ecdh_sha2_nistp256.rb:18:in `test_exchange_keys_should_return_expected_results_when_successful'

Unfortunately, I struggle to find the right equivalent to implement this with immutable pkeys.

Start in lib/net/ssh/transport/openssl.rb around the EC public-key construction and review how the immutable-key error occurs on OpenSSL 3.x. Run test/transport/kex/test_ecdh_sha2_nistp256.rb and use its failing exchange test to verify the supported equivalent is implemented and the key exchange succeeds.