Construction: make fencing ring require 8 oak planks rather than 8 steel kiteshields

What has been done in this MR?

• make fencing ring require 8 oak planks rather than 8 steel kiteshields

What should testers check?

• that building a fencing ring requires 8 oak planks rather than 8 steel kiteshields

• I have tested these changes thoroughly.

• I used the relevant Thanos/Zaros tool for any JSON edits where possible, and have attached screenshots of any changes.