Filter page title (displayed in browser tab) of wp-login

I don’t see a filter in wp-login for the title, but it does use __() so you might be able to use the gettext filter like:

add_filter('gettext', 'wpse_214367_change_login_title', 20, 3);

function wpse_214367_change_login_title( $translated_text, $untranslated_text, $domain ) {

     if( "Log In" == $untranslated_text  )
            $translated_text = "My New Title";

   return $translated_text;
}

EDIT: Please try this and let me know if it works. May also need to add a check to make sure you are on wp-login.php page

 add_filter('gettext', 'wpse_214367_change_login_title', 20, 3);

function wpse_214367_change_login_title( $translated_text, $untranslated_text, $domain ) {
    static $count=0;
     if( "Log In" == $untranslated_text AND $count === 0 ){
            $translated_text = "My New Title";
            $count++;
      }
   return $translated_text;
}