Fix a typo in the script file of the Seraphim Tech 3 Mass Fabricator

[Basilisk3]

Description of the proposed changes

Hopefully this also fixes this warning I sometimes see in replays, but I cannot promise it:

warning: ToggleEnergyExcessUnitsThread: ...\gamedata\units.nx2\units\xsb1303\xsb1303_script.lua(35): attempt to call method `SetSpinDown' (a nil value)

Checklist

• [x] Changes are documented in the changelog for the next game version