Rename Fox Crypto to Sentyron in copyright notices

Rename Fox Crypto to Sentyron in copyright notices

Fox Crypto has been renamed to Sentyron on September 4th 2025.

See https://sentyron.com/press-release-foxcrypto-sentyron/ for the
announcement.

Change-Id: Ic9912627b707bf4edd4fe4bfc37b8a639feaba08
Signed-off-by: MaxF <max@max-fillinger.net>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1047
Message-Id: <20250919164440.23251-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg33102.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>