[3.19] main/libssh2: add mitigations for CVE-2023-48795
add-strict-KEX-to-fix-CVE-2023-48795-Terrapin-Attack.patch
is unmodified https://github.com/libssh2/libssh2/commit/d34d9258b8420b19ec3f97b4cc5bf7aa7d98e35a
https://github.com/libssh2/libssh2/pull/1291
update source URL to https