openbsd: try to bump to 7.7

Author: Mizux

ci/vagrant/openbsd/Vagrantfile

@@ -77,8 +77,12 @@ Vagrant.configure("2") do |config|
   # Ansible, Chef, Docker, Puppet and Salt are also available. Please see the
   # documentation for more information about their specific syntax and use.
   # note: clang installed by default
+  #
+  # Vagrant provide a openBSD 7.4 box while only 7.6 and 7.7 are still
+  # maintained by openBSD -> older registry have been shutdown.
   config.vm.provision "env", type: "shell", inline:<<-SHELL
   set -x
+  sysupgrade -R 7.7
   pkg_add -u
   pkg_add git cmake
   SHELL