pam: fix typo try_authtok → use_authtok
    
    This was a copy/paste mistae apparently, there's not "try_authtok" and
    this was supposed to copy what Fedora uses, which uses "use_authtok"
    correctly. Hence adjust this.
    
    Fixes: #19369
    (cherry picked from commit 971c07fc6812315c2b27015dfcc652a747f919ed)