Update LibreSSL to 3.7.0 in Github actions

Update LibreSSL to 3.7.0 in Github actions

The version 3.5.3 triggers undefined behaviour with the usan sanatizer.
Updating LibreSSSL to 3.7.0 does unfortunately does not fix the issue but
at least we are now using a current version.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20230130172936.3444840-3-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26105.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>