test_options_parse: Add test for read_config_string

test_options_parse: Add test for read_config_string

The <inlineopt> test discovered the issue
fixed by commit "buffer: Fix buf_parse eating input".

Change-Id: Icb91d9c560b6f78f16571ac3052cc566d94afe99
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1247
Message-Id: <20251008100222.4610-1-gert@greenie.muc.de>
URL: https://sourceforge.net/p/openvpn/mailman/message/59243809/
Signed-off-by: Gert Doering <gert@greenie.muc.de>