Fixes <https://bugs.gnu.org/44808>.
Reported by Christopher Lemmer Webber <cwebber@dustycloud.org>.
* gnu/services/ssh.scm (true-but-soon-false): New procedure.
(<openssh-configuration>)[password-authentication?]: Change default to
'true-but-soon-false'.
* gnu/installer/services.scm (%system-services): Explicitly set
'password-authentication?' to #f.