Documentation states that the key
host - hostname or is supported since 4.0.9 URL (as scheme://host:port/path, where only host is mandatory). However:
bash-4.4# zabbix_agentd -V
zabbix_agentd (daemon) (Zabbix) 4.0.9
Revision 97a69d5 5 June 2019, compilation time: Jun 10 2019 08:14:20

Copyright (C) 2019 Zabbix SIA
License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it according to
the license. There is NO WARRANTY, to the extent permitted by law.

This product includes software developed by the OpenSSL Project
for use in the OpenSSL Toolkit (http://www.openssl.org/).

Compiled with OpenSSL 1.1.1b 26 Feb 2019
Running with OpenSSL 1.1.1b 26 Feb 2019
bash-4.4# zabbix_agentd -t web.page.gethttp://google.com
web.page.gethttp://google.com [m|ZBX_NOTSUPPORTED] [HTTP get error: cannot resolve http://google.com]

However test show otherwise.
Tested on official zabbix docker images.
on 4.0.10 http:// works fine.