The system variable OctopusSkipFreeDiskSpaceCheck does not work, see the following raw log error I got for a project that only executes a script in which the following variables are present:
Unfortunately I am not able to reproduce this at this point because we manually cleaned up old files in the server, but I tried all of those options to overcome the problem when it was occurring with no avail.
You should be able to reproduce this easily on your side.