In https://gitlab.com/gitlab-org/gitlab-runner/-/merge_requests/3074, we added a configuration value `[runners.ssh.disable_strict_host_key_checking]` in the config.toml that controls whether or not to use strict host key checking with SSH. Before 15.0, this value defaults to `true`. If it's not set, we disable strict host key checking (which is how it has been up to the change in https://gitlab.com/gitlab-org/gitlab-runner/-/merge_requests/3074). Starting in 15.0, we want the default value of `[runners.ssh.disable_strict_host_key_checking]` to be `false`, so that it's required by default.