(#20607) - do not fail saving lastrunfile when mode is specified

The current settings system to specify the mode of "settings" file
is quite forgiving, but the method (replace_File) used to save
the last run summary file wasn't.
Hopefully with the help of the symbolic_file_mode system, we're now
able to send replace_file a correct file permission mode.

Signed-off-by: Brice Figureau <brice-puppet@daysofwonder.com>