CI: Test experimental ruleset ruleup after its rename to goldkeep
I think that when https://www.hostedredmine.com/issues/820965 renames experimental ruleset as goldkeep in master, CI will no longer make ruleup test for S3_1 experimental ruleset towards master, as there's no ruleset by that name in master's ruleset_list.txt.
Figure out how to make it to work again.
Attached patch that I tested - resulting in a failure.
The problem is that the upgraded ruleset doesn't get written to a directory named "experimental", and so the game.ruleset reference to "experimental/README.experimental" breaks. Those rulesets that are present also in master get around similar problems by luck, as then such files (typically the README) is found from the master's own ruleset.