Support SNI

This fixes connecting using TLS 1.3 to imap.gmail.com

[Fix GH-2077] [Feature #15594]

From: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67488 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/net/imap.rb

@@ -1530,6 +1530,7 @@ module Net
       end
       @sock = SSLSocket.new(@sock, context)
       @sock.sync_close = true
+      @sock.hostname = @host if @sock.respond_to? :hostname=
       ssl_socket_connect(@sock, @open_timeout)
       if context.verify_mode != VERIFY_NONE
         @sock.post_connection_check(@host)