Raise Net::OpenTimeout when TCPSocket.open raises IO::TimeoutError.

With the changes in ruby/ruby#15602, `TCPSocket.open` now raises `IO::TimeoutError` when a user-specified timeout occurs.
This change updates #connect to handle this case accordingly.

Author: shioimm

lib/net/http.rb

@@ -1676,7 +1676,7 @@ def connect
       begin
         s = timeouted_connect(conn_addr, conn_port)
       rescue => e
-        e = Net::OpenTimeout.new(e) if e.is_a?(Errno::ETIMEDOUT) # for compatibility with previous versions
+        e = Net::OpenTimeout.new(e) if e.is_a?(Errno::ETIMEDOUT) || e.is_a?(IO::TimeoutError) # for compatibility with previous versions
         raise e, "Failed to open TCP connection to " +
           "#{conn_addr}:#{conn_port} (#{e.message})"
       end