E1S4: Apply the new balancing changes only on Wesnoth 1.11.7+

This affects the AI and gold configuration changes to this scenario from
commit a345e44feeb9fb955b87446148fb7288f201373a. Since the commit was
prompted by a playtesting run under the new AI recruitment gold saving
aspect enabled by default on 1.11.7 and later, it might be best to
restrict the changes to that version in order to avoid breaking balance
for every other release, including the 1.10.x series, at least until
our support for those reaches EOL.